A summer beach party at Crater Lake takes a dramatic turn when Lois (recurring guest star Erica Durance) hits her head while jumping into the lake. Before Clark can save her, a mysterious swimmer named AC (Alan Ritchson) comes to her rescue, out-swimming Clark and leaving him baffled. Professor Fine (recurring guest star James Marsters) tells Clark that Lex is behind a covert weapons manufacturing operation. AC breaks into a LuthorCorp facility in an attempt to destroy one of Lex's dangerous experiments and is captured by Lex.