This pre-Code comedy-thriller centers on Robert Holden, a broke and discouraged veteran, who meets fellow American Elinor Green at a cafe in Paris. After their first encounter, Holden's attempt to return Green's thought-to-be stolen purse ends up rendering him a stowaway on board a ship bound for America. Also aboard is a collection of characters, including Green's banker fiancé, a famed scientist, and an opera singer. Romance begins to blossom between Holden and Green, just as a radiogram claims that an “infernal machine,” or bomb, is aboard the ship. Quickly each passenger accuses the others of planting the bomb until eventually Holden, jealous of Green's attention to her undeserving fiancé, falsely admits to being the culprit. In his role as assumed perpetrator, Holden tests the group further.