The movie begins with a young couple, Kate, and Justin, eagerly preparing for the arrival
of their first child.
They live in a charming apartment building in London, and are extremely happy as they
anticipate the joys of parenthood.
Kate calls her mother to let her know the scan went well, but no one answers, so she
leaves a voicemail.
During a dinner with friends, Kate and Justin mention about their new neighbours who have
moved into the downstairs apartment.
There is a sense of mystery surrounding these newcomers, as their arrival coincides with
the death of the previous tenant, an elderly man.
Kate also reveals that she still possesses the keys to the apartment, having once tended
to the old man's flower garden.
Here a strange connection begins to emerge when a man listens in on them talking about
how amusing the new tenant's garden looks.
As Kate and Justin return home from dinner, they notice two pairs of shoes outside the
downstairs apartment, signalling the arrival of their new neighbours.
Inside her apartment, Kate stumbles upon an old photograph of herself as a child, alongside
her mother and another young boy.
She is lost in her thoughts when she is interrupted by a sound in the garden, which draws her
attention to a pregnant woman named Theresa.
As fate would have it, Theresa is leaving her apartment at the same time, and the two
women meet for the first time.
Kate shares that she is 18 weeks along in her pregnancy, while Theresa is slightly ahead
at 21 weeks.
Kate then reluctantly accepts Theresa's invitation to join her for swimming.
The bond between them begins to grow, despite an underlying sense of secrecy.
Theresa confides in Kate, revealing that she has chosen the name Peter for her soon-to-be-born
son, but asks Kate to keep this information to herself.
Afterwards, Kate calls her husband and suggests they go out to lunch, and then get a hotel
room, but he is too busy with work.
After she's done with work, Kate spots Theresa while shopping in a children's clothing store.
She follows her until she sees Theresa greeted with a long kiss by her husband, Jon, who
opens the car door for her and they drive away.
Later that night, Justin and Kate are hosting a dinner for their new neighbours to help
them settle in.
Suddenly, the lightbulb in the hallway goes out, and the husband is too preoccupied in
the kitchen to change it before Theresa and Jon arrive.
The first time the two couples meet, everyone gets along great and Theresa tells them that
Jon is German and a successful businessman.
As the two men look out the window, their wives talk at the table, and Theresa tells
Kate that her husband was previously married to a Chinese woman, but she couldn't have children.
While Jon is not looking, she finishes a glass of wine.
As they continue with dinner, Kate and Justin, who have been married for ten years, say they
are not sure if they ever wanted children.
The other couple found this news surprising, as they had both struggled for seven years
to have a child.
Once again, Theresa keeps drinking wine while her husband is not looking, even though she
said she stopped drinking.
When she starts to feel unwell, the couple decides to go home.
However, tragedy strikes as she opens the door, and a tipsy Theresa trips over Kate's cat.
Theresa falls down the stairs, injuring herself.
Kate and Justin, concerned for her well-being, offer to call an ambulance, but Jon reacts
aggressively, blaming them for inviting people over when their house is not safe.
The incident leaves everyone unsettled, and raises questions about the true nature of
the relationships involved.
The next morning, Kate and Justin attempt to contact Theresa and Jon, but their repeated
knocks on the door go unanswered.
A sense of unease and mystery surrounds the absence of their neighbours.
Amidst the uncertainty, Kate and Justin visit Kate's mother, sharing an ultrasound scan
of their unborn child.
The encounter brings mixed emotions, as Kate longs for her mother's support, but feels
a growing distance between them.
Upon returning to their apartment building, Kate and Justin are startled to find Jon waiting
outside the downstairs apartment.
He extends an invitation, welcoming them into their home, and curiosity and trepidation
tangle as they step inside.
Inside the stylish apartment, Theresa, surrounded by an air of sadness, reveals that she prematurely
gave birth to her baby, displaying a photograph as proof.
Kate blames herself for not changing the lightbulb, believing it could have made a difference.
Jon then becomes enraged and tells them that if the lightbulb had been changed, his son
would still be alive.
Kate's husband comes to her defence, telling Jon that it was an accident, and that Theresa
had been drinking wine that night.
Hearing this, Jon is furious and asks Theresa if she drank, to which she says no, but Kate
confirms that she has seen her drink wine.
Things get heated when Theresa claims Kate is making everything up to protect herself,
and with a menacing look, she tells her she does not deserve to have her baby.
Haunted by Theresa's accusations and her own self-doubt, Kate becomes consumed with guilt.
She tells her husband that when she saw Theresa sitting there, she felt ungrateful for ever
being uncertain about having a child, and Justin assures her that their child is the
most important thing in their lives.
A few days later, Kate and Justin find a letter under their door, and in the letter, Theresa
expresses their decision to return to Germany to break the tension between them, and to
grieve the loss of their child.
They vow to return only when they are ready to offer their congratulations.
Time passes, and Kate gives birth to their child, whom they name Billy.
However, she is disappointed that her own mother didn't come to the hospital, so Justin
reassures her that nothing else matters now aside from the baby.
When Kate goes downstairs to grab some milk the next day, she sees shoes outside the downstairs
apartment, meaning that Theresa and Jon are back.
Seeing this, Justin expresses his desire for an apology from them for what Theresa said.
While collecting the birth certificate for their newborn child, Kate gets a phone call
from her mother.
She comes over to their apartment to see the baby and gives Kate a gift, senses a lack
of sincerity in her mother's gestures upon visiting the newborn, only doing so because
Justin asked her to, and not on her own behalf.
They then hear a knock on their door, and find Jon and Theresa standing there.
The couple extend an apology and offer a gift, hinting at a desire to move on from the past.
An air of uncertainty and tension lingers, tinged with a sense of impending danger.
During the visit, Theresa asks to hold Billy, and Kate reluctantly agrees.
In the midst of this uneasy interaction, Kate's mother resists the urge to hold her grandson.
The next day, after Kate's husband leaves for work, Theresa comes to visit Kate with
a glass of lemon juice, and Kate understands that Theresa wants to see Billy.
They spend the day together, going to the park and the swimming pool.
Appearing innocent on the surface, Kate's instincts tell her something is amiss.
As Theresa suggests babysitting Billy, Kate's desire for a break, and some time with her
husband outweighs her reservations, leading her to accept the offer.
Afterwards, Kate is again staring at an old photograph of herself and her mother, her
gaze fixed on the young boy in the photograph.
She then accepts Theresa's offer to babysit, and tries to find solace in revisiting her
past at the cemetery.
There, she mourns the loss of a boy in the photograph who turns out to be his brother,
leaving flowers on his grave and yearning for her own son, Billy, to have the chance
to meet him.
In the meantime, Theresa is seen placing tissues on her breasts, and leaving the house with
Billy, but where she takes him isn't revealed.
When Kate gets back, she finds Theresa just emerging from her nap, and assumes everything
is fine.
Later on, Kate's emotions overwhelm her as she witnesses Billy's relentless crying, and
she seeks medical help to find the cause.
The hospital visit provides a clue about Billy's distress, pointing towards a potential allergy.
Kate is advised to stop breastfeeding and modify her diet.
Upon returning home, they find the gas stove left on full blast, even though Kate remembers
turning it off.
The days blur together as Kate battles exhaustion and an overwhelming sense of fatigue.
Doubts and fear begin to gnaw at her sanity, and to make matters worse, the car alarm from
the couple downstairs keeps going off in the middle of the night.
Her memory falters, and she forgets about Theresa's offer to babysit.
In order to give Kate a chance to sleep, Theresa decides to bring the baby downstairs, but
then she takes the baby outside with Jon without telling Kate.
Later, Kate and Justin are invited for dinner at Theresa and Jon's apartment, and anticipate
a reprieve from their demanding lives as parents.
But Kate seems to be jealous of how Theresa looks in front of her husband, and she goes
to the bathroom to calm down.
Meanwhile, Theresa and Justin engage in an unsettling, yet subtly flirtatious conversation,
fueling Kate's suspicions and discomfort.
Increasingly consumed by paranoia, Kate hears strange
man’s breath noises emanating from the baby monitor.
She frantically runs upstairs, and then discovers the baby peacefully sleeping and an overflowing bath,
but her claims fall on sceptical ears.
Doubt and suspicion cast shadows over her, as Justin believes that she is the cause of
these unsettling incidents.
In a desperate attempt to uncover the truth, Kate requests that Theresa look after Billy
while she goes out.
But instead, she sneaks upstairs, and looks out her window to see what Theresa's gonna
do with her baby.
And to her surprise, she finds Theresa taking pictures of her son, and then proceeds to breastfeed.
Kate then acts like nothing had happened and takes her son back from Theresa, as Theresa
is going swimming as well as meeting her husband for lunch.
After she leaves, Kate grabs the spare key she had from the time the old neighbour lived
there and, determined to find evidence, heads to Theresa’s apartment to investigate.
Her search leads her to the camera, which is filled with pictures of Theresa posing
with Billy.
She then walks into a fully furnished baby room, and discovers a photograph of Theresa
and Jon holding her son, and posing for the camera as though he were their own.
The shocking revelation sent chills down her spine, and as Kate absorbs the weight of the
discovery, she hears Jon's arrival and instinctively escapes back to her own apartment.
The woman immediately calls Justin, demanding his return.
After the husband returns, Kate's urgency leads to a confrontation as she storms inside
Theresa's house to grab the camera she was looking at earlier, but it holds no evidence
of the incriminating photos.
She then barges into the baby room, where she also finds nothing out of the ordinary,
and it's just not like what she saw earlier.
She admits that she was in the apartment earlier, and confronts Theresa about taking pictures
of her son, to which she replies by handing Kate a framed photograph of Billy that she
has prepared as a gift for her.
Returning to her apartment with a heavy heart, Kate grapples with the realisation that the
evidence she found has vanished.
Kate is questioning her own sanity, as her husband Justin remains sceptical.
Justin is staying home to work from home and to check on Kate, as he believes Kate is making
all of this up given her family history.
The wife can't accept that her own husband is not on her side, so she takes Billy out
for a walk.
Along the way, Kate stops at a river to process everything that is happening.
She's just staring at the river, lost in her thoughts, and then she gazes at her baby,
telling him how much she loves him.
Justin is standing behind her, and they converse and come up with a decision to find a different
place to rent, hoping that a change of scenery will bring relief from the torment they've endured.
They manage to locate a lovely new apartment where they can raise their child, much to
Kate's relief.
While driving back, Kate expresses a desire to move immediately, but Justin informs her
that the credit check procedure will take a couple of days, so Kate makes Justin promise
not to tell the unsettling couple anything.
The following morning, Justin suddenly receives a phone call about an important meeting he
was to attend, so he leaves the anxious Kate on her own.
He hands Kate the milk, which she's often seen drinking, and tells her to call the moving
van for tomorrow.
Unfortunately, when Justin reaches the office, he discovers there is no urgent meeting.
But as he checks his computer, he notices an email from Kate stating she's "so sorry,"
and he rushes home, terrified.
Meanwhile, we see Kate and her son Billy, back at the river she was standing by earlier.
She suddenly picks the baby up and throws him inside, watching as the water consumes him.
Afterwards, we see Justin run upstairs to find his wife has taken her own life by overdosing
on medication, and drowning herself in the bath.
He then looks for Billy, but he is nowhere to be seen.
Panicking, he checks if Billy is with Theresa, but he is not there either.
He runs to the nearby river where he found Kate earlier, to see an empty baby carriage.
When he finally realizes what's happened, he drops to the ground and breaks down in
despair.
In the next scene, we find Justin at a funeral, where he is joined by Theresa and Jon.
After the funeral, Justin is packing everything into boxes, as he is leaving that cursed apartment,
not wanting to stay there a minute longer.
Theresa informs him that they are also moving after all the events that have happened.
Here, when Theresa returns to her apartment, the flashback finally reveals the truth about
what took place.
When Kate's husband left for a meeting that morning, he handed her the milk, which she
drank right away, and then she started to feel dizzy and was about to pass out.
Opening the window to get some fresh air, she sees Theresa looking back at her with
a sinister expression on her face.
It turns out that the menacing couple drugged Kate's milk, which is always left outside
the apartment by the delivery man.
They had arranged a fake meeting for the husband, and also sent the fabricated suicide note
from Kate's email.
So what happened to Billy?
Afterwards, we see Kate taking her baby to the river, and tosses him in.
But surprise surprise, it is revealed to be not Kate at all, it's freakin' Theresa, who
has changed her looks to look like Kate.
Then, we see Theresa approach Kate, who is only partially awake.
The final scene shows Jon and Theresa in their new home in Germany, where it is revealed
that Theresa didn't throw Billy in the river; instead, she threw Kate's cat, which is what
made Theresa fall down the stairs before.
Billy, now known as Peter, is alive and lives under the care of his new psychopathic, murderous family.