The Absent-Minded Alchemist (2012)

From publisher blurb:

The Absent-Minded Alchemist is a short (2 encounter) side trek or delve for a group of of level 1 characters, compatible with the Dungeons and Dragons 4th Edition game system. It is designed to be used at any time, and can be inserted in to any campaign if you want something to entertain the party or serve as a means of gaining more information by helping a local NPC.

The great alchemist Zaelin has made quite a reputation for himself in these parts. Although he makes quality alchemical mixtures, potions and other items he is noticeably absent-minded and, in some cases, careless about how he goes about creating these mixtures. He’s had his share of accidents, ranging from injuring half a dozen apprentices to destroying a large portion of his home.

Most recently Zaelin has gotten in to the nasty habit of disposing of his failed mixtures simply by pouring them down the drain. Over time these highly volatile mixtures have eaten through the city’s sewer system and accumulated in the ground beneath his feet. There, the other smaller residents of the city – the countless rats that live underground – have been exposed to these alchemical mixtures and have been the victims of some rather nasty side effects.

Now Zaelin has a problem: his basement is full of rats, but these aren’t the normal rats he’s use to. They have been infused with alchemical energies by his own hand, and they are too many of them for the hapless wizard to deal with himself.

If only a group of adventurers could come by and deal with the problem...