The Lone Wolf in London

Inspector Garvey suspects Lanyard because he is the reformed jewel thief known as the Lone Wolf, and the diamonds were stolen from a Scotland Yard vault. Although Lanyard claims he was in New York when the theft occurred and is in London to write a book about jewels, Garvey believes Lanyard's criminal past makes him the prime suspect despite lacking proof.

Iris Chatham, the celebrated stage star, was the true thief of the Eyes of the Nile. She orchestrated the entire robbery and then killed Henry Robards when he tried to steal the diamonds from her. The diamonds were sewn into the lining of her mink coat.

Henry Robards was found dead behind the wheel of his car with the stolen jewels still in his possession, but the Eyes of the Nile were missing. Iris Chatham killed Robards to retrieve the diamonds he had stolen from her after she had originally received them from him.

Robards was hopelessly in love with Iris Chatham, who had run off with Monty Beresford. When Kelmscott gave Robards a packet of jewels to deliver to Lanyard as collateral for a loan, Robards seized the opportunity to steal the Eyes of the Nile for Iris, hoping to win her favor.

Jamison earlier told Lanyard that Robards was heartbroken because Iris had run off with Monty Beresford.

Lanyard found the diamonds sewn into the lining of Iris Chatham's mink coat while searching her dressing room at the theater. After the airport confrontation, Jamison brought Lily and the mink coat to Lanyard, who extracted the Eyes of the Nile from the coat's interior, proving Iris was the thief.

At the theater, Lanyard had already discovered the diamonds were sewn into her mink coat before Iris escaped.

Sir John Kelmscott was in desperate need of money, though the exact source of his financial trouble isn't fully detailed in the summary. Lanyard suspected Kelmscott was being blackmailed by the thief who sold him the diamonds, which explains his urgent need for a confidential loan using his jewel collection as collateral.

Monty Beresford financed the lavish stage production that launched Iris Chatham to stardom, and Iris ran off with him. At the airport, Monty arrived wielding a gun and declared that Iris had planned the entire robbery and then killed Robards for the diamonds, attempting to shift blame to her.

Iris Chatham stole the Eyes of the Nile for financial gain. As a stage star who had been financed by Monty Beresford, she evidently wanted the valuable diamonds for herself, leading her to orchestrate the heist, manipulate Robards into stealing them for her, and then kill him to recover the stones when he tried to keep them.

Lanyard was cleared when he recovered the Eyes of the Nile from Iris Chatham's mink coat at the airport and turned her over to Inspector Garvey. Monty's arrival and accusation that Iris planned the robbery and killed Robards further exonerated Lanyard, proving he was innocent of both the theft and the murder.

At the London Airport, Lanyard confronted Iris as she tried to flee the country. He turned her over to the waiting Inspector Garvey. Monty arrived with a gun and accused Iris of planning the robbery and murdering Robards, leading to her arrest with the recovered diamonds as evidence.

Iris Chatham called Lanyard to the theater and asked him to stay away from the Kelmscott family because she was concerned that his investigation into the jewel transaction would uncover her involvement in the diamond theft. She needed to prevent him from getting too close to the truth.