The Hegemony Consul (hint: this is a person, we won't learn his name until the very end of the book) is chilling on his spaceship, listening to classical music (Rachmaninoff to be exact), when his fatline receiver chimes. Um, does that hurt?
Not exactly. It's kind of like a holographic telephone call. Sort of a "Hegemony Consul, you're our only hope" from Meina Gladstone, the CEO of the Hegemony Senate, who's pretty much the democratic ruler of the whole galaxy.
Turns out the Hegemony Consul isn't exactly the galaxy's only hope; he's one of seven. Seven people chosen to go on a pilgrimage to return to Hyperion as a member of the Shrike Pilgrimage. Don't worry: we're not sure what that is yet either.
Did we mention he'll be flying on a giant space tree to get there? He'll meet the other six pilgrims on the Templar treeship Yggdrasil.
Not only that, but one of the pilgrims just might be a traitor, an agent of the Ousters (whatever those are).
So what's the point of this whole journey? Gladstone says, "It is essential that the secrets of the Time Tombs and the Shrike be uncovered. […] If the Ousters conquer Hyperion, their agent must be eliminated and the Time Tombs sealed at all cost. The fate of the Hegemony may depend on it" (Prologue.21)
That sounds serious.
The Consul accepts the challenge. He cranks up some Wagner and sets off to rendezvous with the Yggdrasil.