Luthor's Deep-Sea Danger

"Lex Luthor is up to no good! He's trying to dig up deep-sea Kryptonite. Batgirl and Supergirl rush in to end his operation, but deadly green dust fills the cavern, draining the Girl of Steel's powers. What's worse, the tunnels are at risk of total collapse! Can the two Super Heroes stop Luthor's scheme before they're trapped beneath the waves?"--