After her father is killed by the Professor, who got his moniker by mathematically planning his illegal activities, Mollie Riley takes over operation of his gambling ship, the Casino Del Mar , with the help of his right-hand man Tony Garzono. Mollie has just returned from school in Europe, and intends to continue supporting the orphanage named after her mother with the money from the ship, just as her father did. Unknown to Mollie, the Professor is plotting to get rid of her and take over the ship, which operates in competition with his ship. He hires Larry to gain Mollie's confidence. Although he appears to be a gambler, Mollie trusts Larry, and despite Tony's protests, she hires him to work in the galley. Under the Professor's orders, Larry helps Cramer fix the tables on Mollie's ship, and the next night, Mollie loses so much money that she is forced to close. She finds out Larry works for the Professor and dismisses him, even though she has fallen in love with him. Larry films a meeting with the Professor in which the Professor admits to having killed Mollie's father, and he reveals that Larry is actually a special investigator for the state. The Professor holds Larry hostage, and Mollie manages to get the film and have it processed, but does not start to view the film until she has set up a party for the orphans on the ship. Larry escapes from the gangsters in time to throw a bomb they had set on the ship overboard, thereby saving everyone's lives. The Professor and his men are arrested, and Larry and Mollie pursue their romance.
