Alerted by a night watchman, the Chicago police rush to a robbery at the Securities Building. At a side entrance to the building, Lieutenant Bill Mason runs into a cleaning lady with a scarred face. Bill and the cleaning lady's photo is snapped by reporter Ann Rogers, who is unaware that the woman in the photo is actually Slade, the leader of the thieves. Ann follows Mullen, one of the gang members, to an auto court, where she watches as he stuffs $8,000 into an envelope and addresses it to Mary Jordan at the Leonard Sheldon Hotel in New York. Soon after, Bill arrives to arrest Mullen, and Mary shows him the envelope. To trap Slade, who he believes is a man, Bill decides to mail the letter and await his prey at the Leonard Sheldon. Bill refuses to let Mary join him, but when he arrives at the hotel, he discovers that she is working in the mailroom. At the hotel, Bill is joined in his investigation by Lieutenant Onslow of the New York police force and Seidel, the house detective. Meanwhile, also in New York, Slade and her gang comb the classified ads, looking for a secret code about fox terriers that will alert them that the cash has arrived. Upon spying an ad regarding the delivery of the dogs to Mary Jordan at the Sheldon Leonard Hotel, Slade arranges for Ruby, the girl friend of gang member Lefty Landers, to pose as Mary and claim the envelope. Before Ruby is able to make her claim, however, newlyweds Mary and James Powell register at the hotel, and Jim asks if there is any mail addressed to his wife, whose maiden name is Mary Jordan. Thinking that the envelope contains a wedding check from his uncle, James is surprised to find a pile of cash. Financially strapped, he decides to keep the money until his uncle's check arrives. Soon after, Ruby enters the lobby to register as Mary Jordan. Realizing that she is being watched by the police, she runs to Lefty, who is waiting outside in the car, and they speed away. Bill forces their car off the road and takes them to headquarters, where Ruby, in exchange for a promise of leniency, tells him about the dog code, explaining that Slade's name is "great dane." After planting a classified requesting that a great dane be delivered to room 1608, the Powells' room number, Bill wires the room with a dictagraph. As he and Ann listen to the Powells exchanging loving endearments, Bill realizes that he has fallen in love with Ann. When Onslow calls from police headquarters to inform him that Lefty has divulged Slade's address, Bill goes to follow the lead, leaving Seidel and Ann behind to guard the Powells. Slade has already taken the bait, however, and sneaks into the hotel. When Bill and Onslow arrive at the hideout, they find only gang member Matt Willis, and Bill phones Seidel with instructions to protect the Powells. Deciding to take matters into her own hands, Ann pulls a gun on Seidel and orders the Powells into her room while she awaits Slade in room 1608. Slade, disguised as a maid, enters the room, and in a struggle, throws Ann to the floor. Meanwhile, Bill has returned to the hotel, and after hearing the struggle on his dictagraph, breaks into the room with a pass key. After Slade takes Bill by surprise, Ann, who is lying on the floor next to her gun, grabs the weapon and shoots the criminal. All ends happily as Ann gets her story and Bill proposes marriage.