A strange sickness afflicts the frontier settlement of Holver's Ferry, threatening to overwhelm its citizens with an alien madness. Already the town has nearly torn itself apart, and the local sheriff is missing. When the PCs brave the surrounding wilderness as the village's latest newcomers, the beleaguered townsfolk desperately turn to them for assistance. But can these erstwhile heroes trace the diseased carrier to its source and solve the mystery before they, too, succumb to The Assimilation Strain? The Assimilation Strain is a 42-page introductory adventure for the 5th Edition of the world's most famous roleplaying game which can be played as a standalone fantasy horror adventure for 1st-level characters or as a prelude to the Legendary Planet Adventure Path, introducing heroes from any fantasy world to the cosmic threat of alien invaders from beyond who see nothing on this planet but another world to conquer. The adventure blends exploration and negotiation alongside elements of horror and a desperate battle to survive against a foe bent on their enslavement or extermination. The interplanetary adventure continues with the downloadable Legendary Planet Player's Guide and in the sequel adventure To Worlds Unknown, launching your heroes into a fantastic universe of exotic pulp adventure! The sword and planet genre comes to life on Legendary Planet!