In London, Mary Herries, a wealthy and kindly old maid who lives in a large mansion, shows her Christmas spirit by inviting homeless artist Henry Abbott into her home for some tea. Henry, a confidence artist, graciously accepts Mary's offer, but soon exploits Mary's generosity by staying for a sandwich and a cigarette. Lucy Weston, Mary's sister, who has come to take Mary to a Herries Christmas reunion in the country, leaves when Mary complains that she is not well enough to travel. After accepting Mary's hospitality, Henry admires her art collection, and she realizes that he has an educated eye for paintings. Rose, Mary's maid, is uneasy about the strange man, and after he leaves, she tells her mistress that he is too good-looking to be begging for tea, and that surely he is up to no good. When Mary notices that her silver cigarette case is missing, she considers the possibility that Henry stole it, but dismisses the thought as soon as Rose agrees with her. Following a visit by Phyllis, Mary's niece, and her fiancé, Peter Santard, Mary is visited by Henry, who has come to return her cigarette case and apologize for pawning it. Henry then begs Mary to buy one of his paintings, which she does, before asking him to leave and never return. Disregarding her request, Henry plays on Mary's sympathy by showing her the pathetic sight of a poor woman holding a baby outside her window in the rain, and telling her that the woman, named Ada, is his wife, and that the baby is theirs. Mary takes pity on them, invites them in, and then sends Henry to get a doctor to treat Ada's exposure. The kind lady agrees to let the Abbotts stay until Ada recovers, but Henry again takes advantage of her and invites the Edwardses, friends of Ada's, to move in also to Mary's house. Shortly thereafter, Mary decides to rid herself of her unwelcome guests by telling them that she has decided to take a vacation in America, and that she plans to close down the house while she is away. After sending Lucy a letter informing her of her vacation plans, Mary arranges to have Ada taken to hospital. The Abbotts refuse to leave, and together with the Edwardses and a doctor, they conspire to fleece Mary. Henry tries to fool Rose into leaving the house, but when he later discovers her still inside he kills her. Henry, Ada, the doctor and the Edwardses keep Mary in her house at gunpoint, and when Mr. Roubet, a French art dealer, visits, she tries to alert him as to her situation by slipping him a note while her captors are out of sight. Her attempt fails, however, when Roubet turns the note over to Henry on his way out. When the Santards pay Mary an unexpected visit, Mrs. Edwards answers the door and lies to them about the kind lady's whereabouts, telling them that she has gone to America. Later, Peter's suspicions are raised when Lucy tells him that she has not received any word from her sister, and that Mary had terrible guests at her home when she last saw her. When Peter discovers that Mary has neither applied for a passport nor set sail from England, he goes to the constable and tries to obtain a search warrant for the house, but his request is denied because he is not a police officer. Meanwhile, Mr. Foster, a representative from Mary's bank, prepares to sign papers that will turn over all of Mary's assets to Henry. Before they sign, Mary succeeds in slipping him a note explaining her distress, but when Henry and the doctor discover that Foster has been tipped off by Mary, they close in on him and prevent him from leaving. Peter eventually succeeds in getting the police to raid Mary's house, which they do in time to prevent Mary's captors from stealing her money.