His skull began to buzz in the old, familiar way, but he was constitutionally certain that no gate was due to open today. He grinned suddenly, transforming in a blink from serious businessman to imp of mischief ready for some fun.

"Unstable gate!" he crowed, racing into the Commons, even as warning klaxons blared. What would it be this time? Another peek into the late Mesozoic? No, the buzzing of his skull bones wasn't intense enough for a gate that big. The eerie, nonsound told him that this would be a smallish gate, open for who knew how long? Would it cycle several times, then vanish, or set up a steady, long-term pattern? Where? Kit wondered, having seen everything from giant pterodactyls to murderous Welsh bowmen stumble through unstable gates.

Kit arrived a few instants earlier than Pest Control, with their innocuous grey uniforms and staunch faces, discontinuity detectors sweeping the whole area. They also carried rifles, shotguns, and capture nets to be ready for whatever roared through. Mike Benson and several of his security men raced up next, followed by a puffing Bull Morgan. Mike looked terrible-eyes bloodshot, bags under them so dark a purple they looked nearly black, jawline unshaven. Bull looked sharply at his Chief of Security as well, then snapped out, "Any ideas?"

Pest Control's chief, Sue Fritchey, always had a quiet, almost demure air about her-and it often fooled people. Sue was twice as strong and at least four times as smart as she generally looked. Kit chuckled silently. There she stood, looking exactly like a carbon copy of all the other Pest Control agents. You'd never guess to look at her that she held doctorates in biological/ ecological sciences, nematological/entomological sciences, had large- and small-animal veterinary and zoo degrees, and a paleontological science Ph.D to boot: in both flora and fauna. With a master's in virology thrown in for good measure.

Sue Fritchey was very good at her job.

A shimmering in the air opened ten feet above Time Tours' Porta Romae gate platform-and about four feet to one side of it. The air shimmered through a whole doppler range of colors and indescribable motion, then the dark, ever-shifting edges of an unstable gate slid open. Little yellow-brown things fell through it, all the way to the concrete floor below, where they smacked with a bone-cracking sound. A flood followed them, a tidal wave. Kit widened his eyes when he realized what it was. He laughed aloud. "Lemmings!"

Pest Control tried desperately to stem the flow at the gate, using nets to capture and toss back as many as possible while leaning dangerously far over the rail of Porta Romae's gate platform. For every batch of five or six they caught and hurled back, twelve or fifteen more got through, falling messily to their deaths on the now enormous pile of silent, brown-fin-red bodies. Tourists, aghast at the slaughter, were demanding that Pest Control do something, it was cruel, inhuman

Kit interrupted a group of five women dressed in the latest Paris haute couture, all of them badgering Sue while she tried to direct one group at the gate, tried to get another squad into position from a different angle, and put a third squad to work shoveling the bodies into large bags.

"'Scuse me, ladies," he smiled engagingly, "I couldn't help overhearing you."

They turned as one, then lost breath and color in the same moment as they recognized him. Kit hid a grin. Sometimes world-famous reputations weren't such a curse, after all.

"Mr.-Mr. Carson?"

He bowed. "As I said, I couldn't help but overhear, your conversation." He drew them adroitly away from Sue Fritchey a few steps at a time and was rewarded with Sue's preoccupied smile. "Are you ladies by any chance acquainted with the behavior patterns of the ordinary lemming?"

They shook their heads in time, well-practiced marionettes.

"Ah ... let me help you understand. Lemmings are rodents. Some live on the Arctic tundra, where predators generally keep their populations in check. But they also live in cold, alpine climates like you'd find in, say, the northern tip of Norway. Without sufficient predators our sweet little rodents breed out of control, until they've destroyed their environment, not to mention their food supply" Five sets of eyes went round. "When that happens--and it does to many a herd of lemmings, I assure you-then something in their genes or maybe in their brain structure kicks in and causes them to leave their environment, sometimes by the thousands. You see, that unknown signal is a warning that their population has become too large for the land to sustain it. It's as unstable as that gate up there."

He pointed, and waited for five sets of shocked eyes to return to him. "So they leave. Now, the herds that live in very rocky country, with lots of cliffs, have the perfect suicide mechanism built right into their habitat. Some of those cliffs drop into deep, jagged valleys. Some shadow a deep, narrow bay. One full of water," he added, not sure that their collective IQ's were above those of alive lemming. "And you know what those cute little buggers do? They run straight for those cliffs, almost as though they knew, wanted, to throw themselves and their pups over the edge. Those," he pointed to the avalanche of small rodents still falling through the gate, "have jumped off a cliff somewhere. They'd be dead already, even if the gate hadn't opened ten feet over the station floor. You can't change history-or the deep genetics of certain species. Fool about with their genetic structure, get rid of the signal-if you could-that triggers the suicidal migrations, and pretty soon you'd be hip deep in starving lemmings. And there wouldn't be anything green left for thousands of square miles."

Round eyes stared at him from pale, pinched faces. He tipped an imaginary hat and left, humming a delighted tune under his breath. He gave out a short, humorless bark of laughter, wondering what those five would say when they went back uptime?

He then joined the crew sweeping bodies into containers supplied by shopkeepers and other willing 'eighty-sixers. Kit found himself scooping warm, still little bodies into an ornate brass wastebasket that could only have come from the Epicurean. Delight. Kit grinned, then got to business filling it. He sighed. It was a shame; lemmings were so darned... cute. But their biology and behaviors were as they were, which meant that on this particular day and time in La-La Land, Kit Carson was shoveling up hundreds of dead rodents, same as everybody else on volunteer duty. Really, anything was better than attending pointless meetings!

Of all people, Goldie Morran appeared in the crowd, sniffing disdainfully but eyeing all those lemmings with speculation. What in God's name was she up to now? Hadn't she been in the infirmary recently? Didn't take her long to recover. I sometimes think Goldie's too mean to die. She turned on a stilt heel and sought out Sue Fritchey, who listened intently for a moment, then nodded impatiently and shook Goldie's hand. The look on Goldie's face as she tried to figure out where to wipe her hand, covered now with blood and lemming hair, was priceless. Then, when she leaned over an intent newsie's vidcammer and cleaned her hand thoroughly while asking him sweet-voiced questions to distract him from the motions she was making against his back, it was almost too much to bear.

In fact, when one film crew caught it on camera, Kit did laugh-but softly enough Goldie couldn't possibly hear him.

Whatever she'd wanted, she'd clearly gotten, as she left with a contented smile on her face. Kit worked his way toward Sue.

"What'd Goldie want?"

"Hmm? Oh, hi, Kit. She wanted the skins. Said she'd pay a downtimer to skin 'em and tan the skins for her, then maybe the big sternbergi might take a fancy to lemming meat. God, I hope so. Have you got any idea what it's going to smell like, all through the station, if we have to incinerate these little beasts?"