Legends of the Dark Knight (Legends of the Dark Knight Vol. 2 #3)

BAD NIGHT, GOOD KNIGHT PART 3! The Joker is dying from the chemicals he was going to use to wreak havoc in Gotham. Batman only has enough anti-toxin left for one person. Does he save his greatest foe? It sounds like a mortality riddle... what other villain could be waiting for Batman to fail?!