While stopping at the Bronzegilt Hotel, Slick and Slim, two high-class and well-dressed burglars, overhear Baroness Vodka tell the manager she wishes to place her million-dollar box of jewels in the hotel vault, which is set into the wall at the end of the hallway. The manager accordingly escorts her to the big safe, and she watches him place the little box inside. Next morning the manager goes to cash a check for the Baroness, and finds the whole vault has completely vanished. Frantic, the bewildered manager telephones the Tubbs National Detective Agency. Tubbs himself, with Billy and Constance, his wonderful assistants, reach the hotel in a jiffy. He posts Constance in the cloak-room, Billy disguises as a bell-hop and Tubbs as the head waiter. Constance finds a compromising letter in one of the crooks' overcoats, and Tubbs overhears some of their plans. Billy, by lightning disguise changes, learns of a package in Slim's possession marked "dynamite." He is nearly cornered in the crooks' room, but escapes by ducking into the nearest refuge, which happens to be the laundry chute. Billy takes a slide to the cellar, where he hears hammering above him. His suspicions are confirmed when he later gains admission to Slick's room and finds the dynamite. Tubbs discovers that the length of the inside room, compared with the hallway where the safe had stood, varies considerably. Investigation discloses that the burglars have simply put up a blind wall in front of the safe, then deliberately proceeded to break into it. The false wall is battered down and after a sharp fight, the crooks captured. As it turns out, the Baroness is recognized as a well-known female crook and the jewels found to be paste. She was in league with the burglars and planned to recover money for her lost "diamonds."