After she has used up the money left her by an aunt to pose as an heiress and live the life of a London socialite for a year, Lila Banning is about to marry the elderly Sir George Boomer for his money when Cyril Shayne, whom she loves, proposes.

At the Hotel Knickerbocker, when Cyril learns that Lila cannot even pay for their tea, he reveals that he also has no money and leaves her.  Reginald Armstrong, who has eavesdropped on their conversation, buys Lila tea and takes her to a film, after which he proposes that she pose as his wife and go with him to Lake Como, Italy to visit John Graham, one of the world's richest men, whom Armstrong's father staked in the South African diamond fields.  Lila refuses at first, but when the sight of a mouse in her new room repulses her and men in her new neighborhood try to pick her up, she accepts Armstrong's offer.

Meanwhile, Mr. Blake of Scotland Yard informs Graham that the real Armstrongs are in America and that the couple about to arrive are impostors who intend to steal his diamond collection.  Graham, who welcomes excitement, graciously acts the host and grows fond of Lila, while she learns about the scheme of her "husband," whose real name is Morgan, and plans to leave.

Believing that Lila is involved because of some deep unhappiness, Graham tries to prove her innocence to Blake through a test by revealing to her his safe combination.  Morgan overhears it and steals the diamonds, but when Lila tries to replace them, Blake and Graham catch her and Graham angrily denounces her.  Lila, however, is overjoyed to hear Graham admit that he earlier loved her.

After Morgan is captured trying to escape, Lila's innocence is proven, and she and Graham are reconciled.