From the back of the book:
Infinite Worlds . . . Infinite Adventure!
The good news is, there are other Earths. The bad news is, somebody out there doesn't like us.
The shuttles of Infinity Unlimited jump between parallel Earths, seeking profit, knowledge, and adventure. But a parallel called Centrum also has the technology to cross between worlds . . .
and they want to rule them all. The Infinity Patrol must
deal with these ruthless rivals, as well as with world-jumping criminals, and try to keep the secret of dimension travel out of the hands of the really nasty alternate worlds like Reich-5.
Welcome to the core setting of GURPS Fourth Edition! Any campaign can be on one of the Infinite Worlds timelines . . . whether they know it or not! Compiled by Kenneth Hite, the master of alternate histories, GURPS Infinite Worlds combines and updates material from GURPS Time Travel, GURPS Alternate Earths, and GURPS Alternate Earths 2 into one full-color volume, and gives dozens of new worlds to explore as well!
This book also gives detailed rules for time travel, with three different campaign frames.
Whether you’re playing accidental travelers or the hardened troops of the Infinity Patrol, this book is your gateway to adventure. Infinite adventure.