Collision With Chronos — Barrington J. Bayley

The alien ruins that dotted Earth's landscape were an enigma.

Archaeologist Rond Heshke dismissed as a ridiculous hoax the photographic evidence which suggested that the ruins disobeyed the laws of time. The Titanium Legions believed that the ruins had been left behind by an invading force from space, which had been repelled in a past age and whose imminent return was feared.

It was not until the Titanium scientists perfected their time machines that the truth began to emerge piece by piece: that the builders of the ruins belonged not to the stars but to Earth's own future, and that the dreaded confrontation was indeed shortly due - not with aliens, but in a form more horrifying, more calamitous, than anything imaginable...

For Earth was to be the victim of an extraordinary cosmic accident. Time itself was about to collide! Mankind's leaders became even more fanatical, pressing on with new plans, determined at all costs to survive...