It was supposed to be trip into the Outer Realms
Isidoros is a veteran Psychonaut, an alchemist that made contact and explored the Outer Realms. He had gone into the Outer Planes dozens of times with his concoctions. One time, he decided to take a trip and mixed his usual concoction, allowing a plane shift. He took the concoction and went to sleep, shifting his consciousness into the Outer Realms. However, he did not wake up for three days.
Concerned, Maki-Maki -- a lizardress -- is seeking help and importunes the PCs. She is distraught and doesn't know who to turn but to experienced veterans to adventuring. All she asks is for the PCs to help retrieve her friend. She will provide for the concoction, if they will gather the materials. Once gathered, the PCs' consciousness are sent into the Outer Realms to find her lost friend. Designed for 10th level.
For the Gamemaster Edit
This adventure is formulated with consideration for at least one psion (from Ultimate Psionics). However, an Alchemist (specifically, a mind chemist or a psychonaut) can substitute for the psion. The group may also find a fighter type, a rogue, a monk, and a cleric or vitalist helpful. PCs using classes and archetypes from Occult Adventures may find the adventure to be fun, but it was made for at least one Psion in mind.
Isodoros has always been an inquisitive, and precocious child. He wanted to know what was beyond life and death itself, and so decided to find out. Isodoros traveled through his life to find out. None of the philosophical schools had an answer, although he had asked them all. He then turned to alchemy for the answer when a man invited him to share a psychotropic trip.
They both traveled to the etherial plane and Isodoros was stunned at the beauty and majesty of the plane of all and nothing. Isodoros then became a psychonaut and studied psychonautics with others including Maki-Maki. He learned all that there needed to know about being a psychonaut over the course of four years. During this time, Maki-Maki had grown very fond of him and she would make sure that he was taken care of during his trips into the outer realms.
Just this time, he made the trip, but hasn't come back. In fact, he's trapped on the outer realms somewhere, and Maki-Maki has been asking around on how to get him back.