On the very night of his wedding, John Klendon is talking to Helen Carter, his fiancée, on the phone, when he is mysteriously shot by a veiled woman. The shot is heard at the other end and the girl goes into hysterics. Henry Hallam, a guest, is an amateur detective and wealthy. He takes up the case, but the only clue is a bit of paper with the scrawl: "It was I," inclining the police to the suicide theory. The next night Hallam finds a man lying in the roadway, whose features remind him of when he was in Spain with the Carters. He remembers a Spanish beauty casting threatening looks at Klendon, and begins to see light. After caring for the seriously wounded man, he leaves him in care of a physician. Helen enters settlement work to forget the whole terrible affair. The unsuspecting girl is lured to an upper room in a tenement by a dark-visaged woman who pretends her baby is sick, and there finds herself confronted by a dead child, a crazy woman and the door locked. The woman by the crib, after a tirade of abuse, tells Helen how Klendon, after refusing to legitimatize their child by marriage, had thrown her over for Helen. The woman then attempt to throw a vial of vitrol into Helen's face, but is prevented, and the two women struggle desperately. Fortunately, before Helen is overcome, Hallam, who has been notified of Helen's foolish act in going unprotected into the tenement, breaks into the room, followed by Carlo, the man Hallam had found in the roadway. The Spanish woman swallows the acid, and dies almost at once, while Carlo, who proves to be an old sweetheart of the dead woman, explains the meaning of the missing note. The missing letters make it read: "It was I-nez (Inez)." This was the Spanish woman's name, and the mystery, now cleared, Hallam tenderly leads Helen away, and long after, when time has healed wounds, the two find happiness as man and wife.
—Moving Picture World synopsis