The explosion was as loud as a 75-millimeter cannon's.

At one second, there had been nothing but dead wet grass and limestone rocks on the edge of the steep hill. A gray torpedo shape appeared as if precipitated by some invisible chemical in the air. The displacement of air caused the boom that rattled down the hillside and the valley and across the distant river and bounced back to the vehicle.

The H. G. Wells I, without moving a micron in space, had traveled from A.D. 2070, Spring, to circa 12,000 B.C., Spring. Immediately after making the long leap in time, it moved in space. The vehicle had appeared two feet in the air and on the lip of the hill. It fell with a crash to the ground and began rolling.

Forty feet long, its hull of irradiated plastic, it did not suffer from the very steep three-hundred-foot descent. It was not even scratched, though it broke off sharp projections of lime-stone, and eventually stopped upright at the bottom of the hill after snapping off a score of dwarf pines.

'That was better than the fun-house,' Rachel Silverstein said in a quivering voice. She smiled, but her skin was almost as pale as her teeth.

Drummond Silverstein, her husband, grunted. His eyes were wide, and his skin was gray. But the blood was returning swiftly.

Robert von Billmann spoke with a very slight trace of German accent.

'I presume it is safe to unstrap ourselves?'

John Gribardsun twisted some dials on the instrument board before him. A slight whirring told of the projection of a TV camera. The view changed from a blue sky with some high white clouds to dead wet grass ahead and, a mile away, the river at the bottom of the valley.

He turned another dial, and the view switched to the hill down which they had rolled. Halfway up, a fox-like animal jumped out from behind a rock.

The camera swiveled. On the other side of the valley was another animal. Gribardsun turned the closeup dial.

'A hyena,' Gribardsun said. His voice was deep and authoritative. 'A cave hyena. Looks like a Kenyan hyena except it's much larger and all gray.'

Gribardsun had paled only slightly when they had rolled. He spoke with a British accent with a very slight underlying suspicion of another. Von Billmann, the linguist, had never been able to identify it. He had refused to question the Englishman about it because he wanted to label it himself. He prided himself on his ability to recognize any of the major languages and at least two hundred of the minor. But he had no idea of what tongue underlay the Englishman's speech.

The screen showed the view behind the vehicle. A tiny figure stepped out from the shadow of a huge overhang of rock. It ran to a large rock and dropped behind it.

Rachel said, 'That was a man, wasn't it?'

'Has to be,' Gribardsun said.

He kept the camera upon the rock, and, after several minutes, a head appeared. He closed up, and they were looking at a seeming distance of ten feet into the face of a man. His hair and beard were light brown, tangled, and long. The face was broad and a prominent supraorbital ridge shaded eyes of some light color. The nose was large and aquiline.

'I'm so thrilled,' Rachel said. 'Our first man! The first human being. A Magdalenian!'

The man stood up. He was about six feet tall. He wore a fur vest, fur knee-length pants, and calf-length fur boots. He carried a short flint-tipped spear and an atlatl, a stick with a notch at one end, which enabled him to cast the spear with greater force. A skin belt held a skin bag which looked as if it held a small animal or large bird. The belt also supported a skin sheath from which protruded a wooden hilt.

Gribardsun looked at a dial. 'Outside temperature is fifty degrees Fahrenheit,' he said. 'And it's fifteen minutes past noon, late May - perhaps. Warmer than I had expected.'

'There's very little green as yet,' Drummond Silverstein said.

Nobody spoke for a moment. They were just beginning to feel the awe that they had expected to feel. The transition and the rolling had numbed them, and the anesthesia of wonder and fright was just beginning to dissolve.

Gribardsun checked that the equipment was operating at one hundred per cent efficiency. He ran through the CAA (checkout-after-arrival), calling out each item to von Billmann, who sat on his left. The German repeated each, and the words of both were taped. At the end of the checkout, a green light flashed on the panel.

Gribardsun said, 'The air outside is pure. It's air that we haven't known for a hundred and fifty years.'

'Let's breathe it,' Drummond Silverstein said.

The Englishman unstrapped himself and stood up. He was six-foot-three, and the top of his head missed the ceiling by only an inch. He looked as if he were thirty. He had long, straight, very black hair, dark gray eyes, and a handsome, slightly hawkish face. The sheer single-piece tunic revealed a body like Apollo's. He was the M.D. of the expedition, a physical anthropologist, an archeologist, a botanist, and a linguist. If England had not abolished titles, he would have been a duke.

Robert von Billmann stood up a minute later. He was six-foot-two, well-built, thirty-five, titian-haired, and handsome in a pale Baltic way. He was the world's foremost linguist, a cultural anthropologist, an art specialist, and had the equivalent of a master of arts in chemistry.

Rachel Silverstein followed him. She was short, petite, and dark but had light blue eyes. She was long-nosed, but pretty. She had Ph.D.s in genetics and zoology and considerable training in botany and meteorology.

Drummond Silverstein was about six feet tall, thin, and dark. He was a physicist and astronomer and was well trained in geology. He was also a well-known virtuoso on the violin and expert on musicology, preliterate and civilized.

Gribardsun turned the large wheel and pushed open the bank-vault-like port. He stood for a moment in the exit while the others crowded behind him. He breathed deeply and then turned his head to them and smiled slightly.

'I suppose I should say something as poetic as Armstrong's words when he first put foot onto the Moon,' he said.

He stepped out onto a narrow strip, the top of a flight of twelve steps, which had slid out when the port was opened. The air was bracing. He sniffed as if he were a great cat, and then he went down the steps. The camera on top of the vehicle had bent over to take in the area of the port because he had set it to track him when he emerged. Its audio was also on. His image and words would be recorded for posterity - if the vehicle returned.

'This is Time's last gift,' he said loudly, looking up at the camera. 'Modern man will never again be able to travel to this point in time. We, the crew of the H. G. Wells I, will do our best to thank Time and Mankind for this great gift.'

The others looked disappointed. Evidently they thought that, if they had been given the chance, they could have uttered more notable words.

Gribardsun went back into the vessel and unlocked a box of weapons. Rachel followed him and removed clothes of some light but very warm material which retained body heat very effectively. Armed and weaponed, and two equipped with cameras the shape and size of American footballs, they moved out. The port had been closed, but the camera on top of the vessel tracked them. They began the steep climb with the Englishman at their head. They were in excellent physical condition, but all except Gribardsun were puffing and red-faced by the time they reached the top.

Gribardsun turned and looked back down. The vessel was small. But it weighed three hundred tons, and it had to be moved back up to the physical point where it had emerged from Time. Otherwise, when the time came to be pulled back to A.D. 2074, the vessel would remain in 12,000 B.C. And so would its crew. The mechanics of time-travel devices required that the vessel, and its original mass within plus or minus ten ounces, be in the exact landing place.