This off-beat tale by Jim Shooter is the first to really make use of Chemical King, a sadly underused character, whose powers were much greater than most people understood. Adventure 377 (Feb 69) also has one good page of psychedelic 60s art.
Brainiac 5 goes all hallucinatory after a chemical attack by thieves from the planet Modo, operating under the aegis of the crime lord Modulus. But rather than take him on, the story goes in a curious direction, as the Legion start charging people for their assistance.
Leland McCauley makes his second appearance, with Superboy charging for rescuing him from a crashing spaceship. This is the last appearance of the character until the 80s.
The purpose behind the acquisition of money was two-fold; to make the Legion an attractive target for Modulus to rob, and also to gather a variety of currencies, of different materials, that Chemical King could use his powers of speeding up (or slowing down) chemical reactions on. He causes a chain reaction among the currencies that turns them into a paralyzing gas, which takes out the criminals on Modo.
The story does point out that the Legion confiscate the loot they find on Modo, and use it to reimburse those they had charged.
With better art, this could have been a memorable tale.