A summer beach party at Crater Lake takes a dramatic turn when Lois (Erica Durance) hits her head while jumping into the lake. Before Clark (Tom Welling) can save her, a mysterious swimmer, Aquaman, a.k.a. AC (Alan Ritchson), comes to her rescue, out-swimming Clark and leaving him baffled. Professor Fine (James Marsters) tells Clark that Lex (Michael Rosenbaum) is behind a covert operation manufacturing weapons. AC attempts to break into the Luthercorp Marine Center in an attempt to destroy one of Lex's torpedoes and is captured by Lex.