Father thinks no rich man's son is a proper husband for his daughter, so he forbids Betty to see Neal. They had a date for the masquerade ball that night, so Betty tells Neal that she will describe his cavalier costume to the cook, who will let him in at the back. But "Slim" Dorgan, crook, overhears this. When he goes to get his costume, Neal sees an old suit of armor outside the shop and the man tells him it is left outside all the time. Betty and Neal get ready for the ball, but as Neal is on his way to Betty's he is waylaid by "Slim" and a pal, who take the cavalier costume from him. "Slim" puts it on and starts for Betty's. Neal thinks of the suit of armor, goes and puts it on. At Betty's, Officer Griffo is making love to the cook, Stella. The costume gets "Slim" in and he finds father counting his money. Neal arrives and catches the pal, watching outside. The crook shoots at Neal. but the bullets have no effect on his armor and the crook runs away. Inside, "Slim'' and father are fighting, and father is knocked out. Neal tries to get in, but is refused admission. Betty has come down and "Slim" attacks her. The pal comes back to warn "Slim"' and is captured by Griffo. Neal gets in and engages in battle with "Slim." Neal bests him and saves Betty just as father comes to. Griffo takes the crooks and father decides that Neal will make a good son-in-law after all.