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In the concluding chapter of S.O.S. Coast Guard, an unconscious Terry Kent (Ralph Byrd) is brought before Boroff (Bela Lugosi), who plans to use him as a hostage in his getaway. But Terry quickly regains his wits, manages to free himself, and is able to lead the coast guard on a final attack on Gull Island. Boroff, however, has planted disintegration gas at strategic places and Terry and the guardsmen are trapped. They are rescued by none other than Jean Norman (Maxine Doyle), who arrives in the nick of time with the counter gas developed by her scientist brother. The gang members are either killed or arrested but Boroff manages to slip away. The villain is tracked down and destroyed by Thorg (Richard Alexander), his ill-treated and vengeful slave, who is armed with one final vial of disintegration gas.