Somewhere in the Multiverse, in a lab distant from the Makers’ Planet, Tunnel Maker, Creator of Bridges, answers an alarm. His inter-universe probe is detecting signals from another bubble universe, indicating that some new high-intelligence alien species is doing high-energy physics and creating hyperdimensional signals. Tunnel Maker knows that, in another bubble universe, the predatory Hive Mind should be receiving the same signals. It is time to make a Bridge . . .

George Griffin, experimental physicist working at the newly-operational Superconducting Super Collider (SSC), observes a proton-proton collision that doesn’t make sense. He chases it down and discovers a Bridgehead, a wormhole link to the Makers’ universe. With help from theorist Roger Coulton and writer Alice Lancaster, he establishes communication with the Makers, only to learn that a Hive invasion of Earth is imminent. As the Hive invasion is destroying humanity, by wormhole the Makers transport George and Roger back to 1987, where they must undertake the task of manipulating the Reagan, Bush, and Clinton administrations to change the future and prevent construction of the SSC.