A pleasure steamer departs a South American port with two contrasting young women aboard whose differing temperaments shape social life on deck: one lighthearted and flirtatious, the other sensible and determined. The reserved captain and a dashing French count draw attention and complicate alliances among passengers. The voyage brings storms, navigational hazards, and baffling incidents that provoke inquiry, temptations, and physical confrontations. As mysteries are gradually clarified through danger and confession, personal loyalties are tested and the ship resumes its course toward home.