The film opens with a scene of a woman named Mary who is in labour.
Her husband, Jack, remains by her side throughout, encouraging her through the process.
After some time of struggling, she succeeds in giving birth to a baby boy.
But the struggle doesn’t end there, Mary soon resumes struggling, as she tries to push
out her second child, the twin.
Unfortunately, the couple don’t get to rejoice this time, for the second baby is stillborn.
In the next scene, it appears that some time has passed and Mary can be seen nursing her
baby boy, Adam, in a nursery room with two cribs.
It is revealed that due to her grief, Mary is still reluctant to dispose of the second
crib.
On the following day, the small family are hanging around their kitchen, having the time
of their lives and gushing over the new house they’re in, which is a gift from the company
Jack works at.
Jack will leaves for work as usual, and Mary stays at home to do her chores around the house.
At this point, Mary learns that the lavish house is equipped with an automated lighting
system, which automatically switches on the light in a room whenever someone walks in.
After finishing her work around the house, Mary decides to take her baby on a stroll
around the neighborhood.
She then runs into her neighbour; the bubbly Rachel, and the two women introduce themselves
to each other.
Rachel reveals that she’s also a mom, and invites Mary to a playdate sometime.
Mary who hasn't met anyone in her neighborhood yet, welcomes the idea with excitement.
The next day, Mary is seen sitting alone in her kitchen when her baby monitor alerts her
of her child crying.
She then tries to listen to it more closely…
Mary is startled when she could hear the sound
of a second baby crying at the same time.
So she rushes to the nursery and immediately checks on the second crib.
But of course, it's empty.
She then picks up her baby boy and tries to calm him down, while quietly trying to stay
rational and dismiss what she thought she had heard earlier.
Later that night, Mary and Jack are having supper in the dining room.
She tells Jack about what happened earlier, and asks him to buy her a more adept baby
monitor.
Jack agrees and proceeds to ask her to dispose of the second crib, a request which Mary immediately
objects to.
On the next night, the couple can be seen acting affectionate and gleeful with each
other, as Jack has granted Mary’s wish by buying her a new, more advanced baby monitor.
They can now see baby Adam through a CCTV camera installed in the nursery.
Later that night, however, Mary is woken up from her sleep by the sound of baby Adam crying
through the monitor.
She jumps in surprise as she sees a figure of a woman walking up to the crib.
Mary bolts toward the nursery and picks up baby Adam, who is still safe and sound in
the crib by himself.
On the next day, Mary sits with Rachel by the lake and the two converse about the struggles
of being a young mom.
The two of them bond over their shared struggles, and Mary lights a piece of Rachel’s cigarettes
for herself.
Later, Rachel invites Mary to a playdate in Rachel’s house.
When Rachel isn’t in the room, Mary discovers that Rachel owns the same exact kind of baby
monitor as her
She then theorizes that perhaps the CCTV signals got mixed up for a second last night, and
displayed Mary a view of Rachel’s crib.
Rachel concurs, saying that these things happen.
As Mary and Jack get ready for bed in the evening, Jack reveals to her that in a week’s
time he’s about to take off on a business trip out of town.
Mary appears a little morose at the news, but gives Jack her blessing.
The next day, while changing the baby's diaper, Jack discovers a strange birthmark on baby
Adam’s left thigh, but brushes this knowledge aside.
That night, Mary yet again wakes up to the sound of her baby crying.
She comes up to the nursery, and cradles him in her arms until he falls asleep.
However, as Mary lays Adam down in his crib,…
she startles to the sound of a baby chuckling
behind her.
She slowly turns around and gasps upon a gruesome sight in the other crib.
When she summons the courage to look into the crib again, she finds that there is nothing
there.
The following day, Jack takes Mary to see a therapist in hopes of getting rid of the
visions she’s had these past few days.
After hearing her story, the therapist concludes that what she’s experiencing is none other
than postpartum depression.
The therapist prescribes her with antidepressants, and convinces her to get rid of the empty
crib.
This time, Mary eventually listens to the advice, and takes apart the empty crib as
soon as she gets home.
Several days pass, and it is revealed that Jack has installed several CCTV cameras around
the house.
When Mary asks about it, he tells her that it is for her and Adam’s safety, so he can
check up on them while he’s away on his business trips.
As a result, the couple ends up arguing, with Mary stating that Jack has lost trust in her,
and that she doesn’t want him to leave her alone for days at a time anymore.
But Jack still argues that he has no choice because it is his job.
On the next day, we see Jack packing up and getting ready to leave for the business
trip, saying he’ll be back in two weeks.
After learning that her husband must leave or someone else will take his place, Mary
watches him leave with a heavy heart.
Mary is now alone with baby Adam at her house, but suddenly...
she wakes up from her slumber when she hears the sound of the nursery window shattering.
She then calls the police over to investigate, and after taking a look around the house,
the detective tells her that she doesn’t need to worry because he’s convinced that
the culprit is a local gang of delinquents.
Plus, this isn’t the first time the gang pulled this sort of stunt.
When Mary hears this, she is skeptical but doesn’t argue.
The next evening, a storm rages outside while Mary sits on the floor, watching the CCTV
footage from the other night.
She watches the footage recorded by a security camera installed inside the room, and could make out
a mist of a figure breaking into the window.
She tries to lean closer to the screen to take a better look…
Mary is now convinced that this entity intends to kidnap her son.
Therefore, she begins searching the internet for any information about mythical beings
kidnapping babies, and finds an article about a woman named Jane Henderson, who claimed
that a demon stole her child.
As Mary reads on, she finds that Jen’s experience was very similar to what she’s been experiencing.
On the next day, Mary visits Rachel and tells her about her odd experiences.
Upon hearing her story, Rachel takes it upon herself to call Jack to update him about what’s
going on.
When Rachel leaves the room, Mary takes another look at the picture of Jane and her baby on
the website from last night.
At this point, she notices that Jane’s baby bears the same birthmark as the one Adam has
on his thigh.
Taking this as a sign, Mary takes off to see Jane.
She arrives at Jane’s house and introduces herself.
Jane appears to understand Mary’s purpose for visiting, and welcomes her in.
After that, Jane begins to tell her about her experiences with the supposed demon; how
she felt like she’s being watched all the time when her baby was around.
Jane then plays a voice recording from the night her baby was taken…
An ominous voice can be heard saying, “the baby is mine.”
Jane pauses the recording before it finishes though, claiming that she still finds it triggering
to this day.
After that, Jane shows Mary an old book containing information about the baby-stealing demon,
and tells Mary to make a choice whether she would let her own baby get taken, or find
someone else’s baby for the demon to take.
Mary doesn’t answer, and on her way back it is revealed that she has the book and Jane’s
recording with her.
Later that night, Mary lies awake in bed, ruminating her options.
She is snapped away from her wandering thoughts, at the feeling of being watched from the gaps
in the vent right above the bed.
On the next day, Mary is seen having a video call with her mother, but suddenly...
the screen lags and shows a scary figure.
Scared, Mary slams her laptop shut and walks away.
She spends the rest of the day studying about the demon, until she falls asleep on the couch.
She is woken up yet again at night by an ominous sound.
She then goes to investigate…
She finds that the sound is coming from the old baby monitor which she hasn’t used in
a while.
The sounds persist, the demon seemingly greeting Mary.
Hearing the demon say her name, Mary takes a recording device to document the conversation
that ensues.
She asks the demon the reason why he is targeting her son.
We don’t get to hear the answer yet, because the film shifts to the next scene, in which
Mary is standing in front of the mirror, looking exhausted and overwhelmed by everything that’s
been going on in her life.
At night, she’s lying awake in her bed, but suddenly...
she hears a strange sound coming from
outside her room.
Mary takes a knife she prepared on her bedside and goes to investigate.
As it turns out, it is Jack who just came home from his trip.
Seeing her wife's messed up condition,
Jack wraps the scared Mary in his arms to comfort her.
On the following night, Mary paces about the bedroom, rambling about her baby who has been
taken by the demon.
Jack fetches baby Adam and tries to convince her that nothing’s wrong.
He is now convinced that her wife’s mental health has seriously deteriorated.
The next morning, however, as Jack is about to leave for work, he is surprised to find
Mary all dressed up and cheerful.
After Jack leaves, Mary is in the middle of setting up a bath for baby Adam right when
she hears Jack’s voice, asking her to open the door for him.
As Mary steps out of the bathroom, all of the sudden the bathroom door shuts and locks
behind her.
She begins to panic, afraid that her baby is going to drown to death.
Since Jack doesn't answer her,
Mary runs out into the street and screams for help.
She takes an axe from a truck parked across the street and uses it to tear the door open.
Finally, Mary sees the mysterious black figure who has been looking for her baby.
Mary wakes up in a hospital with Jack by her side, reprimanding her for her recklessness.
She still defends herself by saying that she’s done all that she could to protect their baby.
Jack who doesn't believe her proceeds to show her the CCTV recording.
Seeing the recorded CCTV, Mary cries and insists that the demon has tampered with the recording.
The frustrated Jack steps out of the room and returns cradling baby Adam in his arms.
He hands Mary a tablet that would enable her to monitor their baby from the hospital.
Jack then says she just gotta get better soon, excuses himself and goes home.
Later that night, Mary is watching the home CCTV, as Jack is putting the baby to bed.
He then goes to open the door,
and Rachel the neighbor is there.
Rachel is welcomed inside and to Mary’s surprise, the two start hooking up.
Mary, however, is more concerned about her baby, so she resumes watching the CCTV in
the nursery.
As Mary finds the demon in there again,
she yanks off her IV line and bolts away from the hospital, back to the house.
Not only does she not find Jack there, the baby is also nowhere to be found.
She then discovers that Rachel is hosting a Halloween party at her house next door and decides to
go there.
Mary finds Rachel at the party and begins reprimanding her, accusing her of sleeping
with her husband.
Rachel asks her to calm down and takes her to the kitchen so they can talk privately.
Rachel then continues to deny the accusation and tells her that Mary’s husband is away
with the baby, picking up Mary’s mother at the airport. But Mary seems to be acting
even more erratic, going as far as taking a kitchen knife and threatening Rachel with
it.
Mary ends up lying on the floor crying while Rachel steps out of the room to look for help
to handle Mary.
Once Mary is alone, she can hear the sound of Rachel’s baby crying in the other room.
An idea stirs in her mind: she is going to sacrifice Rachel’s baby to the demon.
Soon after, Rachel returns to the kitchen with the police officer from their neighbourhood
but Mary is nowhere to be found.
Rachel then checks her nursery and finds that her baby is gone as well.
It turns out that Mary has returned to her own home with Rachel's baby, sitting on the floor with a knife
in hand and cries out of guilt.
Rachel and a number of neighbors rush to the huge window by Mary’s side, begging her
not to harm the baby.
Seeing Mary is out of control, Rachel decides to call Jack and tells him what’s going on.
She puts him on a loudspeaker for Mary to listen to.
When Mary hears Jack's voice, she insists that she isn’t crazy and that she’s only trying to protect her son.
Jack tells her to wait for him to get home, and that he is on his way now.
Convinced that she is talking to a demon disguising himself in her husband’s voice, Mary raises
her arms and moves to kill the baby.
Right in time, the police officer manages to shoot Mary in the chest preventing her
from harming the baby.
Jack returns home a few moments later to find his wife lying dead on the floor.
Some time has passed, and Jack is now taking care of the baby alone.
He had just put baby Adam to bed right when he found the recording Mary made of her conversation
with the demon.
At this point, Jack eventually learns the truth about what had happened behind his wife's
erratic mental state.
The demon told Mary to sacrifice any baby in order to save her son.
We can see that Jack now regrets not listening to his wife before.
Then all of the sudden, the light in the room across the hall switches on.
Jack, who has a strong sense that something is wrong, goes to investigate and enters the nursery.
He looks into the crib and the film ends without revealing to us what Jack sees.