Two English crooks, Lionel Verker and his sister, Marie, come to America, where at a seaside resort Lionel makes a heroic rescue by saving Bob Kent, the son of a millionaire, from drowning. He is introduced to the Kent family. Learning that there is a position of lady's maid open in the house, he wires his sister to come at once. With the aid of false references she obtains the position. At a lawn fete Muriel, the daughter of the millionaire, wears a lot of jewelry. Lionel notices this and after a dance with him she misses one of her diamonds. Notwithstanding the fact that he does not suspicion any of his guests, Papa Kent advises the famous detective, Donald Bryce, that he had better come. He is introduced as a guest. Bryce perceives Lionel and Marie in secret communication and also perceives Lionel slip Marie a note, which tells her that he is going to the city and that if anything happens, to telegraph him, using the cipher code. Bryce obtains the note and although he cannot read it, he watches Lionel closely and when the crook makes a hurried departure the next morning the detective follows him. In the city Bryce shadows Lionel. One day he perceives a cipher message from Marie. On his way to the railway station he stops at a café, where he eats a light repast. Bryce follows him and does likewise. In his hurry to get out, Lionel takes the coat belonging to Bryce and departs, while the detective takes that of the crook. He finds the cipher message and hurriedly makes a copy of it, and places the coat back on the hook. Lionel notes the mistake he has made in taking the wrong coat and rushes back to the café with it. He takes his coat, makes a hasty examination of the pockets for the cipher message, finds it and is soon on his way to the seaside. Bryce goes to his office, where, upon deciphering the code, learns that Miss Kent is to wear expensive pearls on Friday. Just before he leaves to go to the Kent mansion, he opens his foreign mail and finds a letter from the English authorities enclosing descriptions and photographs of the notorious crooks, Lionel and Marie. It is not long after that Bryce has the crooks where they belong.