Post Season Four. Lex comes back to life and power. Lois, knowingly, of her own free will, and free of any mind control or any other extraordinary influence, willingly has sex with Luthor. Explain why. Maybe a minor change in time Tempus didn't even realise he'd set in motion for example. Show the fallout for her and Clark. Have it split at some point into two possible endings. 1 is where L&C get back together and all is good for the world, utopia is intact, etc. 2 is where Lois & Lex end up together, Lois turns evil, they kill Clark, the world is screwed and utopia never happens.
