A U. S. Navy lieutenant finds the murderer who is sabotaging the cruiser's new fire-control system.
On a cruiser Lt. Tom Randolph (Robert Taylor) asks for liberty but is refused. Captain Winslow (Arthur Byron) tells the officers they are installing a new fire-control system so that foreign competitors won't get it. Spud Burke (Nat Pendleton) gives Toots Simmons (Una Merkel) a ring she can keep if he doesn't show up at seven. Civilian Mac O'Neill (Ted Healy) wants to take out Toots too. Randolph meets engineer Al Duvall and civilian inspector Victor Hanson (Jean Hersholt). Betty Lansing (Jean Parker) comes aboard to find Randolph and tells him that her wealthy father has a great job for him; but he feels obligated to the Navy. Spud sees his ring on O'Neill's hand, and they bicker. A crate falls and injures a sailor; the winch was sabotaged. The Manchukan Consul (Mischa Auer) comes aboard with his secretary. Toots tells O'Neill that the $50 he gave her for the ring is no good, and she gets the ring back for Spud.
Jeffrey from a gyroscope company tells Randolph they have better fire-control gear and offers him $25,000 if the installation fails. Randolph orders him put off the ship. While a salute is fired, someone shoots Duvall. A woman is found with a gun. She wanted to kill Bill Williams because he had agreed to marry her; but this is resolved when he promises to do so. Everyone is held on board. Randolph tells Captain Winslow about the inventor Hanson and the bribe offer from Jeffrey.
Someone stabs the electrician Johnson. Spud arrests the sailor in the armory. The reporter Drake wants to get the story out but cannot leave or use the radio. Captain Winslow questions Jeffrey about the bribe and locks him up. Visitors must stay overnight. Men work at night, and Drake is shot while trying to leave the ship and is brought back slightly wounded. Betty apologizes to Randolph, and he kisses her. Spud talks gently to Toots and gives her the ring. Spud discovers a hot cable, and Randolph calls "Collision quarters." Williams tells Randolph that someone hit him. Randolph finds Hanson, who threatens to ignite the gunpowder. He and Randolph fight, and Williams calls for help while flames spread. A man turns on the water, putting out the flames; but Randolph and Hanson continue to fight as the water rises. Finally Randolph knocks Hanson out and opens the door. The Manchuko Consul thanks Captain Winslow and leaves the ship, and Winslow congratulates Randolph. Randolph kisses Betty good-bye, and O'Neill can't see Toots because he has been hired for the cruise.
This story reflects U. S. naval preparations and in retrospect ominously portends the Japanese threat. Capitalist and foreign competition appears to endanger military security.