Pretty much what the title says. Lex constructs some device intended to harness the life energy of his other selves across the multiverse, thereby making himself a god. Meanwhile, in another universe on the opposite end of the multiverse, Rick Sanchez creates a similar device intended blah blah science technobabble. Somehow, these two end up getting their wires crossed and as a result Rick Sanchez ends up stepping into Lex Luthor's life and place in the DC verse. Everyone ends looking and seeing him for the man that they know Lex Luthor to be, including Superman. Sooner or later, Rick gets fed up with all these caped and spandexed losers sticking their noses in his business and decides to put them down as Lex Luthor would.
How well does Rick do in Lex's place?