Ripping Time by Robert Asprin & Linda Evans

The departures in line hastily gathered up their luggage. Those still at the customs tables scrambled to pay the astromical taxes demanded as a condition of departure. Then the savage lash of subharmonics which heralded the opening of a major temporal gate struck Skeeter square in the skull bones. A fierce headache comprised of equal parts low blood sugar, stress, and gate subharmonics blossomed, causing him to wince. Skeeter resisted the urge to cover his ears, knowing it wouldn’t shut out the painful noise that wasn’t a noise, and simply waited.

The sight was always impressive as Primary opened up out of thin air. A point of darkness appeared five feet above the Commons floor. It grew rapidly, amoeba-like, its black, widening center an oil stain spreading across the air. The outer edges of the dark hole in reality dopplered through the whole visible spectrum, with the spreading fringes shimmering like a runaway rainbow. A stir ran through the spectators. Every person in the station had seen temporal gates open before, of course, but the phenomenon never failed to raise chill bumps or the fine hairs along the back of the neck as the fabric of reality shifted and split itself wide open . . .

A flurry of startled grunts and a rising flood of profanities sounded behind them. Skeeter turned to crane his head above the crowd. “Aw, nuts . . .”

Literally.

The Angels of Grace Militia, at least the portion that had escaped arrest during the riot, was on a crash-course drive for Primary, shoving their way through by brute force.