Mr X, a hospital patient, wakes up completely disoriented. His doctor, Professor Llewellyn, tells him that he is in Wales and has been in a car accident, which has left him physically unharmed but with part of his memory gone. Assuming that the memory loss is due to a personal crisis, Llewellyn conducts a series of tests to discover the identity of Mr X. Little is revealed, so he traces the car back to a London hire firm, who agree that the model is missing and claim they can identify their customer.
Llewellyn and Mr X drive to London where the people at the car hire confirm his identity. With new contact details, the duo drive to Mr X's Hampstead home and are greeted by his maid and dogs. Llewellyn, who has to leave for an important meeting, informs Mr X's wife, Monica Hendricks, of his condition. She tries to restore his memory by explaining that they have been married for five months, and that he has a job at the Ministry of Munitions. She adds that his friend, Jack Carter, sent a message last Thursday explaining that her husband had been instructed to go to Wales by his boss, J.F. Hassett. All this information means nothing to Mr X and Monica gets upset. She forces him to sleep in the spare bedroom, but quickly forgives him.
The next morning, the couple go to the Ministry so that Mr X can ask for sick leave while he is recovering from his memory loss. He tries to find Hassett to clarify why he was sent to Wales but Hassett says that he will only continue to talk to him at their gentleman's club, the Adelphi. It soon becomes clear that Mr X doesn't work at the Ministry, and he is asked to leave. He goes to the Adelphi to wait for Hassett, and receives surprised looks from the other members. At the bar he finds Jack Carter, who explains to him that last Thursday night Mr X had assaulted one of the waiters, throwing him over the balcony. Understanding the outraged looks from the other members, Mr X decides to leave but, once outside, two men hustle him into a car. They identify themselves as the assaulted waiter and Luigi Sopranelli. They explain that he is married to Luigi's sister, Lola, but hasn't been seen for six months. He faints again and wakes at the Sopranellis' restaurant where the family tell him that Lola still loves him. Trying to apologise and leave the restaurant, he inadvertently upsets Lola and while comforting her they start kissing. He tries to say farewell again but trips and falls unconscious.
The following morning Mr X is given the old clothes that he wore when married to Lola. In a suit pocket, he finds a Charing Cross station left luggage ticket, which he assumes will fill in the details of who he really is. He escapes from the restaurant and, after picking up a trunk from Charing Cross, books a hotel room in which he can look through his belongings.
He is horrified to discover letters from several wives, numerous identities and evidence of gross fraud. Trying to stay calm, he contacts Llewellyn and requests that he return to his Welsh hospital. Llewellyn obliges, and on his arrival informs Mr X of five more wives. He recommends a clean break by confessing to the police, and Mr X happily complies.
The bigamy cases go to trial and Mr X agrees to be defended by a female lawyer, Miss Chesterman. Initially claiming innocence because his actions were taken by a part of him he now finds abhorrent, he soon changes his plea when he discovers that all his wives want him back and are paying for his defence. Not wanting to return to any of them, he chooses to go to prison. After he has served his time, Monica, Lola and the other wives wait for him outside the prison. Charles flees to escape them and is grateful for a car at the end of the road. When he gets inside, he discovers Miss Chesterman waiting to take him away.
