The Solitaire Man

After a job in Monte Carlo, the English jewel-thief ring returns to Paris. Oliver Lane, the suave 'Solitaire Man,' proposes marriage to his partner Helen and reveals the plan to retire to a Devonshire country house. Bascom, unstable and drug-addicted, also loves Helen and resists retiring from crime.

Bascom presents the Brewster necklace he burgled from the British Embassy, signaling that he might be the sole suspect. Oliver realises that arresting Bascom would unravel the whole ring. He returns the Brewster necklace to the safe just as a Scotland Yard inspector arrives at the embassy.

A second man slips into the embassy and steals the Brewster necklace, signaling that the plan is unraveling. The inspector recognises the thief but is shot and killed as the killer escapes. Oliver wrestles with the killer in the dark and grabs the necklace and part of the watch chain.

Oliver hastily decides to flee to England with Bascom, Helen, and Mrs. Vail. They are joined on the airplane by Mrs. Hopkins and a last-minute arrival in the form of an unknown Englishman.

As the plane takes off, Mrs. Hopkins demands that her late-arriving husband be picked up, but fog blocks the plan. The unknown Englishman identifies himself as Inspector Wallace and attempts to arrest Oliver; the group disarms him and Bascom locks Wallace in his own handcuffs.

The passengers learn a supposed French Army escort is following them. Convinced Wallace is a real inspector, Oliver offers to surrender and turn over the necklace in exchange for the others' freedom. He then switches off the cabin lights to throw off the pursuing plane in the fog.

Oliver suspects Bascom tipped off the police; Bascom admits some betrayal but denies carrying out the scheme. Oliver finds Bascom's letter to the police detailing their travel plans, exposing the betrayal.

Overcome by guilt, Bascom leaps from the plane to his death, shocking everyone aboard. The loss confirms Oliver's suspicion that Wallace is deeply involved with the crimes as more than a mere informant.

Oliver, now convinced Wallace is a thief and informer, studies Wallace's pocket watch with a broken chain to confirm his guilt. He uses the clue to threaten exposure and to calibrate the plan with the others.

Oliver stages a dramatic ruse, suggesting he might be involved in a murder while he maneuvers to control the situation. He agrees to hand over the Brewster necklace and confess to the murder only if Wallace tells Scotland Yard the others had no part.

The plane lands at Croydon and is briefly boarded by police, while a second escort plane lands behind them — Elmer Hopkins's plane, sent to retrieve his wife. Wallace tries to depart by pretense, but Oliver insists that he is the true inspector, preventing his escape.

Inspector Harris interrogates the passengers and exposes Wallace as the jewel thief and murderer. Wallace is shot by Harris with an unloaded gun, unaware Oliver has tricked him. Oliver then summons Scotland Yard using the plane's radio, and Harris accepts that Oliver is a legitimate jewelry dealer. Oliver and Helen head to start a quiet life in Devonshire.