Lovecraft's nameless narrator and West start out as medical students (later doctors) at Miskantonic University, where they experiment on fresh corpses with a serum, or "reagent", West developed that revives the bodies. But unintended side effects like homicidal insanity and cannibalism manifest themselves in the revived corpses (zombies) and eventually, after having gone as far as experimenting on severed body parts (like an actual head!), West is undone by his work.
To say more would spoil the grisy and delirious surprises that await you in reading this tale. Fans of Lovecraft's work will note the introduction of certain themes that would reappear in his later work, such as the sense that humans have no control over forces they can't understand, and that personal obsession and desires (however unnatural; as the tale unfolds over a period of years, West continues to revive the dead for little more than his own enjoyment) ultimately results in fatal consequences for all. Oh, and good old Miskantonic U, the school that seems to attract every weirdo in New England, makes the first of several appearances as the setting (or one of them) in a Lovecraft tale. (Wonder if the school had a fight song?)
The recaps that begin parts 2-6 are repetitive (Lovecraft hated them too), yet add to the unfolding sense of unreality and insanity that sweeps the story to it's bizarre conclusion. You get the sense the narrator (who sounds completely gone by the end) is hanging on to what's left of his sanity by repeating and reviewing the previous events when recounting the tale.