To all those time travelers who came before: H. G. Wells, Jack Williamson, Murray Leinster, Robert A. Heinlein, Randall Garrett, and Fritz Leiber most notably; and also to the one among all others who inspires my plots: Niccolo Machiavelli.

It was with mounting frustration that the computers and the experts who controlled them were well primed for nuclear defense, laser defense, outright invasion from space, and all the other exotic ways in which the enemy might inflict damage, yet not totally effective against the slingshot.

Somewhere a siren sounded, and soon a cacophony of electronic warning bells went off throughout the defense complex. Technicians put down whatever they were doing and scurried to their situation boards, but there was little for them to do even with danger approaching. The computers could handle things much faster than they, and all they could do was watch and worry and check the status of the defense systems.

“Incoming!” somebody shouted needlessly. “Oh, my God! Look at that board!”

The main situation screen showed it now: more blips of various sizes than any of them could count, all coming in in a wide pattern. Two blips, however, were enormous.

“What the hell are they shooting now? Planets?” somebody else muttered, the awed question carrying in the sudden silence of the room, now that the warning signals had been cut off.

It was a meteor storm like they had never seen before— tens of thousands of chunks of space junk and debris with only one thing in common—all were at least large enough to survive entry into Earth’s atmosphere. Nor was this a random swarm. Like the rest, it had started out around Jupiter, with the great space tugs of the enemy forming them up and shooting them around with vast energy beams the defenders could only envy, using the gravity of the big planet to whip them around and send them in a predetermined spread inwards to the Earth.