There were timelines branching and branching, a mega-universe of universes, millions more every minute. Billions? Trillions? Trimble didn't understand the theory, though God knows he'd tried. The universe split every time someone made a decision. Split, so that every decision ever made could go both ways. Every choice made by every man, woman, and child on Earth was reversed in the universe next door. It was enough to confuse any citizen, let alone Detective-Lieutenant Gene Trimble, who had other problems to worry about.

Senseless suicide, senseless crime. A citywide epidemic. It had hit other cities too. Trimble suspected that it was worldwide, that other nations were simply keeping it quiet.

Trimble's sad eyes focused on the clock. Quitting time. He stood up to go home and slowly sat down again. For he had his teeth in the problem, and he couldn't let go.

Not that he was really accomplishing anything.

But if he left now, he'd only have to take it up again tomorrow.

Go, or stay?

And the branchings began again. Gene Trimble thought of other universes parallel to this one, and a parallel Gene Trimble in each one. Some had left early. Many had left on time, and were now halfway home to dinner, out to a movie, watching a strip show, racing to the scene of another death. Streaming out of police headquarters in all their multitudes, leaving a multitude of Trimbles behind them. Each of these trying to deal, alone, with the city's endless, inexplicable parade of suicides.

Gene Trimble spread the morning paper on his desk. From the bottom drawer he took his gun-cleaning equipment, then his .45. He began to take the gun apart.

The gun was old but serviceable. He'd never fired it except on the target range and never expected to. To Trimble, cleaning his gun was like knitting, a way to keep his hands busy while his mind wandered off. Turn the screws, don't lose them. Lay the parts out in order.

Through the closed door to his office came the sounds of men hurrying. Another emergency? The department couldn't handle it all. Too many suicides, too many casual murders, not enough men.

Gun oil. Oiled rag. Wipe each part. Put it back in place.

Why would a man like Ambrose Harmon go off a building?

In the early morning light he lay, more a stain than man, thirty-six stories below the edge of his own penthouse roof. The pavement was splattered red for yards around him. The stains were still wet. Harmon had landed on his face. He wore a bright silk dressing gown and a sleeping jacket with a sash.

Others would take samples of his blood, to learn if he had acted under the influence of alcohol or drugs. There was little to be learned from seeing him in his present condition.

"But why was he up so early?" Trimble wondered. For the call had come in at 8:03, just as Trimble arrived at headquarters.

"So late, you mean." Bentley had beaten him to the scene by twenty minutes. "We called some of his friends. He was at an all-night poker game. Broke up around six o'clock."

"Did Harmon lose?"

"Nope. He won almost five hundred bucks."

"That fits," Trimble said in disgust. "No suicide note?"

"Maybe they've found one. Shall we go up and see?"

"We won't find a note," Trimble predicted.

Even three months earlier Trimble would have thought, How incredible! or Who could have pushed him? Now, riding up in the elevator, he thought only, Reporters. For Ambrose Harmon was news. Even among this past year's epidemic of suicides, Ambrose Harmon's death would stand out like Lyndon Johnson in a lineup.

He was a prominent member of the community, a man of dead and wealthy grandparents. Perhaps the huge inheritance, four years ago, had gone to his head. He had invested tremendous sums to back harebrained quixotic causes.

Now, because one of the harebrained causes had paid off, he was richer than ever. The Crosstime Corporation already held a score of patents on inventions imported from alternate time tracks. Already those inventions had started more than one industrial revolution. And Harmon was the money behind Crosstime. He would have been the world's next billionaire—had he not walked off the balcony.

They found a roomy, luxuriously furnished apartment in good order, and a bed turned down for the night. The only sign of disorder was Harmon's clothing—slacks, sweater, a silk turtleneck shirt, kneelength shoesocks, no underwear—piled on a chair in the bedroom. The toothbrush had been used.

He got ready for bed, Trimble thought. He brushed his teeth, and then he went out to look at the sunrise. A man who kept late hours like that, he wouldn't see the sunrise very often. He watched the sunrise, and when it was over, he jumped.

"Why?"

They were all like that. Easy, spontaneous decisions. The victim-killers walked off bridges or stepped from their balconies or suddenly flung themselves in front of subway trains. They strolled halfway across a freeway, or swallowed a full bottle of laudanum.

None of the methods showed previous planning. Whatever was used, the victim had had it all along; he never actually went out and bought a suicide weapon. The victim rarely dressed for the occasion, or used makeup, as an ordinary suicide would. Usually there was no note.

Harmon fit the pattern perfectly.

"Like Richard Corey," said Bentley.

"Who?"

"Richard Corey, the man who had everything. ‘And Richard Corey, one calm summer night, went home and put a bullet through his head.' You know what I think?"

"If you've got an idea, let's have it."

"The suicides all started about a month after Crosstime got started. I think one of the Crosstime ships brought back a new bug from some alternate timeline."

"A suicide bug?"

Bentley nodded.

"You're out of your mind."

"I don't think so. Gene, do you know how many Crosstime pilots have killed themselves in the last year? More than twenty percent!"

"Oh?"

"Look at the records. Crosstime has about twenty vehicles in action now, but in the past year they've employed sixty-two pilots. Three disappeared. Fifteen are dead, and all but two died by suicide."

"I didn't know that." Trimble was shaken.

"It was bound to happen sometime. Look at the alternate worlds they've found so far. The Nazi world. The Red Chinese world, half bombed to death. The ones that are totally bombed, and Crosstime can't even find out who did it. The one with the Black Plague mutation, and no penicillin until Crosstirne came along. Sooner or later—"

"Maybe, maybe. I don't buy your bug, though. If the suicides are a new kind of plague, what about the other crimes?"

"Same bug."

"Uh, uh. But I think we'll check up on Crosstime."

Trimble's hands finished with the gun and laid it on the desk. He was hardly aware of it. Somewhere in the back of his mind was a prodding sensation: the handle, the piece he needed to solve the puzzle.

He spent most of the day studying Crosstime, Inc. News stories, official handouts, personal interviews. The incredible suicide rate among Crosstime pilots could not be coincidence. He wondered why nobody had noticed it before.

It was slow going. With Crosstime travel, as with relativity, you had to throw away reason and use only logic. Trimble had sweated it out. Even the day's murders had not distracted him.

They were typical, of a piece with the preceding eight months' crime wave. A man had shot his foreman with a gun bought an hour earlier, then strolled off toward police headquarters. A woman had moved through the back row of a dark theater, using an ice pick to stab members of the audience through the backs of their seats. She had chosen only young men. They had killed without heat, without concealment; they had surrendered without fear or bravado. Perhaps it was another kind of suicide.