When his ship is delayed in Hamilton, for repairs, sailor Heinz decides to visit Niagara Falls. Bored after his long weeks at sea, he gets an exciting idea — to go over the Falls in a barrel.

A ship docks in a Canadian port with a girl stowaway aboard. Investigating, Nick King and Admiral Fox, are stymied by her refusal to tell them where she is from, or why she has come to Canada.

A murderer is being sought on the docks. He kidnaps the daughter of a ship's captain and blackmails him to take him out of the country. King joins the ship and works out what has happened but stopping the man is more difficult.