Mr. Montgomery Jones, a rich but not so bright man seeks help of Blunt’s agency for a peculiar alibi case. Montgomery met an Australian woman Una Drake and fell in love. While talking about their mutual love for detective stories, she made a bet with him that he cannot shake an alibi she has set for herself. She agreed to give him anything he wants if he manages to solve the alibi puzzle. Intending to ask for her hand in marriage, he accepted the challenge. He seeks Blunt’s detective agency’s help in solving the alibi.
Una Drake sent Montgomery a proof of being present at two distinct places at one time. According to one story, she dined at the Bon Temps Restaurant in Soho by herself, went to the Duke’s theatre to watch Delphiniiums Blue, and had supper with a friend Mr. Le Merchant at the Savoy. But at the same time she was also staying at the Castle Hotel in Torquay, and only returned to London on the following morning. Challenge for Montgomery is to find out which of the two stories is true and how she managed the other.
Theory, Inquiries and finding flaws in alibi
Tommy and Tuppence go through the papers given by Una to Montgomery as proof of her whereabouts for the day in question. Papers confirmed that on that day she dined at Bon Temps at 7:30pm, went to Duke’s theatre and watched Delphiniums Blue, and then had a supper with Mr. Le Marchant. They plan to interview Mr. Le Merchant, though they suspect him to side with Una and not give the show away.
Then they checked papers for Torquay. She left from Paddington at twelve o’clock, had lunch in the restaurant car(bill enclosed), and then stayed at Castle Hotel for one night(bill provided).
They conjecture that the girl only went to Torquay and London thing is fake, as anyone can buy a theatre ticket without actually going there.
To cement their conviction, they interview Mr. Le Marchant who confirms that Una was indeed present with him at the supper. He also tells them about Oglander people at the next table that day.
The meeting with Le Marchant changed their mind and they begin to explore the possibility of Una being present at Savoy for supper that night.
Next they go to Bon Temps to confirm. Not getting anything concrete to conclude anything, they return to their office.
Similarly they visit Torquoy and found most of the proofs of alibi solid enough to neglect.
In the end, Tuppence manages to solve the puzzle. Una has a twin sister, who arrived in England the day before the events.