Our thirteenth downloadable GM-SS Dungeons and Dragons One Shot Adventure – an easy-to-follow introductory session!

Whether it’s for a one-shot adventure, starting a longer story, or just another day in your players’ lives, we hope this adventure module will inspire all you DMs and GMs out there. Our thirteenth adventure module is meant to help DMs to introduce new players to D&D 5e. There are rats to hunt, ancient sewers to explore and crazy magics to avoid. Enjoy!


  • RPG: D&D 5e

  • Number of players: 4 or less recommended

  • Recommended level: 1-3

  • Duration: very short (1-3 hours)

  • Difficulty: very easy

  • For your campaign: This adventure is meant for people who have little to no experience with TTRPGs. Hence, it should be kept as short as possible and most of the rules listed in the document should also remain hidden from the players.

  • This Adventure Module contains: 

    • The story for a single adventure
    • Tips on how to run a introduction session for new TTRPG players
    • Builds for several new monsters
    • Build and Background for a NPC
    • Puzzles and riddles for your party to solve
    • Maps and ideas for special combat encounters

The Story

Like most large port towns with lots of food and bad sanitation, Ghenna has a pest problem. An unusually large rat colony has taken a liking to its scenic waterways and mouldy cellars. Each day, a thousand more furry creatures scuttle through the city’s drainage pipes and sewers. Usually, this isn’t a problem the local royalty would concern itself with. However, after Queen Marissa found rats dancing in her new summer home’s bathroom, the pest problem has been swiftly declared a threat to the crown. Unfortunately, knights and city guards make for bad exterminators and not many sane men are keen to delve through Ghenna’s wild sewers. To make matters worse, the superstitious citizens declared the weirdly smart rats to be the heralds of the demonic forces supposedly living under the city. Hence, the “Reformation through Extermination” act was passed, allowing local law enforcement to pass down fines measured in rat scalps. Captured criminals were allowed to shorten their incarceration by delving into the sewers and bringing back heads or pelts. Needless to say, criminal activity in Ghenna dropped considerably. Not because more criminals were deterred by the sentence, but because most of them never returned from the city’s rat-infested bowels.

In this 1 – 3-hour introductory adventure, a party of 1st level characters are sentenced to reformation through extermination. The task is not only disgusting and arduous, it soon turns deadly. Can they collect enough rat pelts before becoming rat food? Is there a way to stop the infestation altogether? Can they survive being “On Her Majesty’s Pest Control Service?

Notes for the GM / DM

  • This adventure is split into three parts, as it is meant to showcase D&D’s three modes of play – roleplay, exploration (skill checks) and combat. Hence, they should be given equal weight while playing.

  • There are a lot of tipps on what to do for new players before the session begins. However, the adventure works just as well for veteran players.

  • The length of this one-shot can be extended to up to 6 hours, if the entire map provided is used. However, it is recommended to keep it as short as possible for new players.

GM-SS 13 On her majesty's pest control Cover