Here's the plot of the poems/albums in a nutshell
The story begins with a brief overview of significant events from the 16th to 18th century, and introduces the Les Invisibles, invisible all-powerful gods similar to The Great Old Ones in Lovecraft's work. In the late 18th century their messiah, named Imaginos, is born in Mexico, although he won't be aware of who he really is and the scope of his power for a long time. After turning into an adult, Imaginos uses his shape shifting abilities to turn into a buzzard and fly to America. He stops in Texas and then continues his journey to New Hampshire, where he takes a job on a ship heading to Del Rio. The ship crashes and he washes up on the beach, and is left to die by the other surviving members. He lies half-conscience, on the verge of death, when the Blue Öyster Cult, an underwater sect that worships the Les Invisibles, rises out of the water to save him. After nursing him back to health, they tell him who he really is, Desdenova, the Invisibles's Messiah and evil incarnate. He is evil incarnate in the way that just because he exists, war, genocide, and hate will as well. He basically goes mad at this knowledge up until the events of Astronomy where he accepts his status and attempts to pass on the knowledge to Susie, a girl he met at The Four Winds Bar. After this he pretty much ascends to the stars and his influence continues into the 20th century and beyond. The End.
I'm sure someone else can explain it even better, but that's the rundown.
