Infernal Machine Rebuild

Background

Eons ago, a planar craft of unknown origin crashed within the Barrier Peaks. The scholar Kwalish would later find this craft, converting it into his laboratory and studying its technology to fuel his own experiments. However, Kwalish was not the first explorer to do so.

Earlier expeditions also chanced upon the crash site, and although most parties perished while delving through the craft, a few managed to recover rare objects never conceived by even the greatest minds of this world. Many of these objects were subsequently lost over time—and most resulted in the deaths of their owners along the way. But a few persisted, controlled by those able to glean some partial understanding of their operation.

Among the most important of these relics was the planar craft's central command console, used to guide its flight through space and time. Legend of this object grew as it fell into the hands of a warlord and came to be known as a most powerful artifact: the Infernal Machine of Lum the Mad (so named after its last owner). Yet with the defeat of Baron Lum, his Infernal Machine was said to have been destroyed as well.

Currently, the archdevils Zariel and Bel both have designs on rebuilding Lum's infernal machine. Zariel is the present master of Avernus, the first layer of the Nine Hells. Bel is the deposed former master of that layer. But to rebuild the infernal machine, both devils require a number of missing components—former control buttons vital to the machine's operation. Zariel and Bel have both planted agents in the world, tasking those agents with finding adventurers to track down and claim these components. Once the Infernal Machine of Lum the Mad is complete, whichever devil controls it plans to use the machine to claim final dominion over Avernus.

Adventure Summary

While journeying through fey woods, the characters must choose whether to help a trio of (supposed) dryads or a unicorn, with each faction blaming the other for the woods' corruption. Either way, the characters come across a fallen clock tower containing a strange set of magical components, which appear to manipulate time within a localized area.

Discovery of these components leads to an invitation to meet one of two agents: Lynx Creatlach or Sir Ursas. Both are in competition with each another to collect all such missing components, in order to reassemble the Infernal Machine of Lum the Mad. Each agent pledges to use the Infernal Machine against devilish forces plaguing the world—but each secretly plans to give it to their own patron archdevil. Both ask for the characters' help, looking to hire them to undertake expeditions to retrieve the missing components.

Once the characters are involved, they are provided the resources to travel to two legendary locations of the past to recover the Infernal Machine components believed to be there. First is the Tomb of Horrors, in the period while the infamous dungeon is still under construction. There, they meet the tomb's architect, Moghadam, who oversees the site with an iron hand. The second location is the Temple of Moloch in the same era. The temple is run by Moghadam's chief rival, Thessalar—the inventor of the thessalhydra and many other grotesque monsters, including the owlbear.

The characters must navigate the perils of both locations, manipulate time, and manage untrustworthy agents to return with as many of the missing components as they can. And even then, they must contend with the agents who hired them, and ensure that a completed Infernal Machine of Lum the Mad does not fall into the wrong hands!

Running the Adventure

To run this adventure, you need the D&D fifth edition core rulebooks—the Player's Handbook, the Dungeon Master's Guide, and the Monster Manual.

Most of the monsters that appear in the adventure are from the Monster Manual, along with a number of creatures from other books (including Volo's Guide to Monsters and Mordenkainen's Tome of Foes) plus a number of new creatures and NPCs. For easy reference, all the stat blocks for the creatures in the adventure can be found in appendix B. When a creature's name appears in bold type, that's a visual cue pointing you to its stat block in that appendix. Full information on creatures from the Monster Manual, Volo's Guide to Monsters, and Mordenkainen's Tome of Foes can be found in those books.

Spells and equipment mentioned in the adventure are described in the Player's Handbook. Magic items are described in the Dungeon Master's Guide. Where new spells and magic items appear in the adventure, the text directs you to their descriptions in appendix C.

Adventure Hooks

You can bring the characters into this adventure in any way that makes sense for your campaign. Make use of any of the following suggestions, or use them as inspiration.