Clark meets a young man with a power of speed that exceeds his own, but the boy lacks responsibility for his actions. Also, Lex finds a manuscript that appears to be some sort of Kryptonian map.

The Green Arrow sends out for reinforcements and Bart Allen, a.k.a. Impulse, Arthur Curry (Aquaman) and Victor Stone (Cyborg) return to Smallville to help him take down LuthorCorp's secret lab called 'Project 33.1'. During a break-in at the LuthorCorp facility, Bart is captured and tortured by Lex for information to who hired him. Clark sets off to rescue him but is felled by kryptonite. An alarmed Chloe goes to Oliver for help, and the newly formed "justice league" springs into action to rescue Clark and Bart. Meanwhile, Oliver painfully decides to break up with Lois, feeling that his dedication to justice is more important, but he leaves out that information from her.

Clark tells Oliver that he must kill Davis, but Clark deals with the fact that he can't take a human life. This leaves the justice league to take the affair on their own hands. Then, Rokk Krinn teleports from the 31st Century to give Clark another Legion time-traveling ring so Clark can exile Davis/Doomsday to the future. But in a surprising twist, Lois confronts Tess about her nefarious plans involving a mysterious crystal and in the fight, Lois accidentally finds Rokk's ring, and gets zapped into the future. Meanwhile, Chloe gets in the middle of Clark and Oliver's fight about Doomsday's human carnage, in which Dianah/Black Cannary and Bart/Impulse intervene. Jimmy finds out Clark's identity, leading to a fateful showdown when Clark attempts to use black kryptonite to split Davis from Doomsday and seal the beast in a large hole in the ground. But nobody is prepared for what Davis will do afterwords.

As the VRA threat intensifies, Clark takes initiative by closing down watchtower and declaring the League go officially underground, but will this be enough to stop Lt.Trotter and Slade Wilson aka Deathstroke from exposing them? Tensions rise in this mid-season finale.