The movie begins in 1943; World War II deeply entrenched the United Kingdom.
Lieutenant Commander Ewen Montagu, a Jewish attorney, hosts a party and announces during
his toast that he is taking a hiatus from practicing law as he has been appointed
the Naval representative of the Twenty Committee. Ewen gives tribute to his wife,
Iris, and announces that she and their children will leave to be safe in America.
Meanwhile, in the cinema, a British intelligence agent named Charles Cholmondeley goes to take a
seat when he spots his colleague, Jean, a woman who he has been crushing on for
a while. He tries to converse with her, but she's uninterested and waiting for someone.
He goes quiet when her date, an American soldier, arrives at his seat beside her.
After the party, Iris approaches him to remind him they have no choice but to leave,
as their whole family is Jewish and will be in danger if England is attacked. Hester Leggett,
Ewen's loyal secretary, bids Iris goodbye and safe travels as she leaves to prepare for their
early leave in the morning. Hester tells him his wife knows he would put his duty before anyone
else and his own family, so her leaving him is right, even if it hurts them both. The next day,
he says a tearful goodbye to his wife and children as they leave for America.
Elsewhere, British Prime Minister Winston Churchill discusses with Admiral John Godfrey
that he promised the United States that the Allies would invade Sicily by July of that
year to push northward into Europe. However, the Wehrmacht may defend Sicily because it's
an obvious target. They must find a way that Britain must trick Nazi Germany into
believing the Allies would invade Greece. Admiral Godfrey suggests an operation from the Trout Memo,
created by the Twenty committee, to be used. The next day, at Charles's home, his mother
asks for info about Charles's late brother, Robert, who died on the battlefield. He was
one of the British fighter plane pilots that died a week ago on the battlefield. The military
encountered difficulties retrieving his body as he was killed in action in Chittagong, Bengal. Still,
Charles assures his mother that he will find a way to retrieve his brother's body and bring him home.
The Twenty Committee conducted a meeting; Admiral Godfrey informed the Twenty Committee
that Britain must trick Nazi Germany into believing the Allies would invade Greece.
Charles proposes an operation from the Trout Memo, which he dubbed Operation Trojan Horse,
which would entail a corpse carrying false secrets and washing ashore. Despite Godfrey's doubts, he
allows Ewen and Charles to plan the operation with his assistant, Lieutenant Commander Ian Fleming.
After the meeting, Charles, Ewen, and Ian go to an empty office. Ian explains that the Twenty
committee gave them the place to use as their headquarters. Their first task is to obtain the
corpse they will use for the mission while Hester prepares the office and recruits new members.
After days of searching, they still couldn't find a suitable body, Hester suggests her friend's
help, who's a forensic officer, and they manage to obtain the body of a vagrant named Glyndwr
Michael, who died by possible suicidal poisoning. One night at the Gargoyle Club in Soho, Ewen,
Hester, and Charles discuss their chosen corpse. The team gives him the false identity of Major
William Martin, Royal Marines, and uses Ewen's identification number. They decided he must have
finance, and the woman should also work in intelligence to keep the mission a secret,
which reminds Charles of Jean. The next day, Charles approaches
Jean to ask for her cooperation, as William's fake fiancée, for the mission,
which has been renamed Operation Mincemeat. Jean is reluctant, but in the end, she decides to help,
and in exchange, she wants to learn more about the mission. They tried to take the corpse's
photo to make it look alive, but to no avail; all their photos were not convincing enough.
That night, Ewen, Hester, Charles, and Jean go to the bar to look for a man similar to
William to take pictures of. They continue to brainstorm ideas for William's backstory. Ewen
creates the romantic story of how William and his fiancée, which he named Pam, met and fell in love.
Suddenly, an American soldier arrives at their table, per Jean's invite, and they are shocked
by how he looks so alike to William. To keep the operation a secret, they claimed they needed an
American soldier, just like him, for an interview and some photographs, which he agreed on.
Later that night, Ewen escorts Jean back to her house while they plan
the perfect life story of Pam, and they each find themselves in William and Pam.
Two months pass, and they still need to proceed with the operation. Jean offers someone to help
with the pictures, and Ewen offers to escort her there. As they leave, Charles asks what
the female employees are gossiping about, and it's about how Ewen and Jean do not use formal titles
around each other, which he also noted. Later, Charles is called to meet Admiral
Godfrey in his office and updates him on the successful preparation of the mission. Godfrey
suspects Ewen's brother, Ivor, is a spy for Russia. He bribes Charles to spy on Montagu,
and, in return, Godfrey will locate and return his brother's remains, and Charles reluctantly agrees.
Soon, Charles and Ewen discuss Jean and how she's becoming increasingly involved with the mission,
especially with Ewen. Ewen denies it before explaining it further; the morgue called. Glyndwr
Michael's sister, or William as they know him, has come to claim his body, as the hospital staff
informed her of his current whereabouts, as she wants to give him a proper burial. Knowing this,
it might put a dent in their progress. They explain that Glyndwr is employed in a top-secret
mission, and his service will turn him into a hero. They try to bribe her, but it only offends
her, and she leaves their office. With Churchill's approval, they will deploy the mission quickly.
The next day, Ewen recruits two men from the British Embassy based in Spain. Ewen explains
the reason for inviting the two of them is because William's corpse would later be washed ashore in
Spain, and their role is vital in the mission. Their role would ensure that the letters from
William's corpse would land in Berlin. The next day the preparations continue.
Jean makes the love letters written by Pam, which William's corpse would carry, and Ewen makes the
fake documents containing the British attack on Greece more convincing. At the same time,
Charles prepares the plans for transporting the body via submarine to the shores of Spain. Soon,
they successfully convince Admiral Godfrey of the letters and finally complete the
preparations. All they have to do now is to wait for the execution to take place in three days.
They are having a small celebration party at the office, hoping for the mission's success.
Jean reads Pam's love letter they made; they are all entranced with William and Pam's love story,
even if they know it was all made up. After the party, Ewen takes Jean home. Ewen took the eyelash
from Jean's cheek. The action flusters her, making Jean say a quick goodbye and go inside.
The next night, Godfrey meets with Charles. He suspects Ewen's brother,
Ivor, was the Soviet Union spy who helped Germany and wants Charles to investigate.
Charles says he would never betray his friend. Charles reluctantly informs Godfrey he hasn't
found anything proving Ivor to be a Russian spy. The next day, they photograph the letters that
they will send out. Charles notices the officer slipping Jean's eyelashes into the fake document
Ewen had taken yesterday. Charles stays silent but is confused about why Ewen has Jean's eyelashes on
him. Then they prepare the body and put fake papers and letters in the pockets.
After this, Charles, Ewen, Jean, and the driver assigned to the operation, Specialist MI5 driver
St. John "Jock" Horsfall, goes to the bar to devise what the driver should do for the
mission. While Ewen talks to the driver, Charles invites Jean to dance. Jean expresses her interest
in William and Pam's love story. Saying that she dreams of such a thing happening to her,
even though it's a made-up story. After hearing this, Charles realized that Jean must have fallen
in love with Ewen, which they based William on so much. Charles tells her that unlike her,
Hester, and himself, Ewen is lucky enough to have a family to return to.
The reminder sadden her, so she quickly leaves the bar. Ewen sees this and tries to stop her.
When he finally catches up with her, Jean confesses how she had fallen in love with
William's figure inside Ewen and ended up forgetting the reality. She didn't realize
that Ewen had a family in real life. But she tells Ewen not to worry about her,
and he will be late for the mission. Later, Jock transports Ewen, Charles,
and the corpse to the R.N. Submarine Base in Holy Loch. They load the corpse
onto the submarine HMS Seraph, with Lt. Bill Jewell commanding the operation.
After delivering William's corpse, Ewen immediately goes to Jean's house and
apologizes. He knew that deep down, he also has feeling for her. He wishes her the best,
and they both hope for good luck with William's mission. Jean doesn't say anything to respond,
but tears fall down her cheeks after Ewen leaves. Two days pass.
On the morning of April 30, the Seraph arrives in the Gulf of Cádiz and drops the corpse into
the ocean. All the while, the team prays for the mission's success. Fishermen in Huelva, Spain,
soon find the body. Operation Mincemeat attempts to get the fake documents to Madrid. However,
the mission is hampered by bad luck, as the Spanish resisted Nazi corruption better than
expected. Captain David Ainsworth, the British naval attaché in Madrid, meets with Colonel
Cerruti of the Spanish secret police in one last attempt to get the papers to the Nazis.
Days pass with no news about the documents. Everyone's nervous, but suddenly a telegram from
the embassy announces that the papers have been returned and will be sent to England immediately.
After the documents arrived at night, Ewen Charles and the examiner examined
each of William's belongings. Still, they were disappointed because nothing had changed. Even
the royal seal stamp on the letter envelope is untouched. But when they open the letter,
they find Jean's eyelash is missing. When the specialist examined the letter,
it was concluded that it had been opened and reprinted.
Meanwhile, Jean is ambushed and threatened at her home by Teddy, Gargoyle Club's bartender.
He claims to be a spy for an anti-Hitler plot within Germany. She tells him that Major
William Martin is traveling under an alias, but the classified information is genuine.
After Teddy leaves, Jean informs Charles and Ewen of the incident. They believe that Colonel
Alexis von Roenne, who controls intelligence in the Nazi High Command, sent Teddy to verify
information so Von Roenne could undermine Hitler. However, they have yet to be entirely sure.
Outside, Charles finally expressed his feelings that he had liked Jean all this time but chose
to keep it to himself for the sake of the mission. At the same time, Ewen, who had a family, was busy
seducing Jean and missed that Ewen's brother was a Soviet Union spy. Charles suspected that
the bartender must be Ewen's brother's accomplice. Operation Mincemeat might have been leaked to the
Germans. Still, if Teddy told the truth, there's nothing to worry about. Later, Ewen takes Jean to
his home for protection, but she soon accepts a job in Special Operations and leaves London.
On July 10, the Allied invasion of Sicily commenced. The news arrives that the Allied
Forces have suffered limited casualties, the enemy is retreating, and they have successfully held the
beaches. Afterward, Charles admits he received his brother's remains in return for spying on
Ewen. Feeling sympathetic and relieved that Operation Mincemeat is a success, Ewen offers
Charles a drink, hoping to fix their friendship. The movie ends with Ewen reuniting with Iris and
their children after the war. Jean married a soldier, and Hester continued as Director
of the Admiralty Secretarial Unit. Charles remained with MI5 until 1952, later married,
and traveled widely. In 1997, they revealed Major William Martin's true identity as Glyndwr Michael,
and they added an epitaph with his real name to William's headstone in Spain.