Mercury is the first installment of the Tales of the Solar System series.
Dan Peronet and his boyfriend, Rich, are hiking through "The Gardens" in Hermopolis, a colony located on Mercury. It is 3:00 in the morning but the hot sun is shining down on them as they jump in a lake and make out, shortly before Rich breaks up with Dan, calling him a loser. Dan calls his friend Kathy to tell her the bad news. The two decide to play hookie from school. Dan's brother Leon overhears and invites himself to tag along. Dan, Kathy, and Leon skip school and spend the day in downtown Hermopolis. In an alley, they are confronted by a gang of street thugs, with whom Dan picks a fight. Dan and his friends pursue this gang through the streets of Hermopolis, vandalizing things as the day proceeds. Ultimately, Dan meets up with Daloctra, whom the gang is hiding from the authorities. Dan and Daloctra bond and have sex. Daloctra tries to recruit Dan into her movement and he begins to accept her ideology. He tries to get Leon and Kathy on board as well. But Dan soon learns that Daloctra intends to release a biological agent into the city to destroy all life there, returning Mercury to its pre-human existence. This gives Dan pause, and he eventually tries to go to the authorities to have her and her organization arrested. He does this knowing that he and Leon and Kathy will be arrested as well, following the vandalism the day before.
Unfortunately, Dan is too late. Daloctra releases the biological agent. Dan convinces the authorities to release him from jail, along with Leon and Kathy, so that he can help evacuate the city and help the authorities find Daloctra. The agent is taking its toll and by the end of the day, there are no survivors. Dan learns that Daloctra has headed to Venus and he, along with his friends, decide to pursue her.