“River Run” continues: Swamp Thing's odyssey through parallel worlds leads him to a dark bayou where an aged, semiretired superhero must defeat Solomon Grundy and uncover a terrible secret.

In the fourth story of River Run, The Secret of Slaughter Swamp, Swamp Thing must take on the form of Solomon Grundy, and reveal to a semi-retired superhero named the Black Box the secrets of Slaughter Swamp, including one very dark secret belonging to his wife.

Note: This chapter is inspired in the earth-2 concept from the pre-crisis multiverse.