The sub-sea gun which is being perfected by Lieutenant Vane is coveted by Koral, a secret agent of a foreign government, who plots to secure it. Charlotte hears of the conspiracy and, at a skating-rink party, warns Vane, but he takes the matter lightly. From a secret wireless plant Koral is to send a message to Fredericks aboard his yacht. Charlotte cuts the antennae of the wireless apparatus on the boat, thereby preventing the receipt of the message. Fredericks, believing that something has gone wrong with Koral for his failure to communicate, sails, but at sea discovers that his wireless machine has been damaged. Meanwhile Vane finds that his gun has been stolen, and later he receives a note from Charlotte to be at the pier. The authorities are informed, and when Fredericks returns he runs into the arms of the law. Koral and his confederates are also taken prisoners.