Porsupah was somewhere behind. Being capable of swimming circles around any of them, it was decided that he should follow at a distance. This would enable him to give them a little time if any pursuit should develop. That beggared the fact that there wasn’t a thing they could do about such pursuit, but it seemed too reasonable an idea to ignore.

Somewhere up ahead their youthful guide felt for a gate that might or might not be charged with lethal current. She took another breath. He’d been right about the tides. In some places there wasn’t enough room to get one’s head above water. In such spots she had to turn on her back. Then she would drift with only the upper part of her face above water, sometimes scraping the cold stone of the roof as she drew in long draughts of moist, stale air. Then it was turn, dive, and swim, heading for the next air pocket, pushing off the wall for a little extra distance and hoping she wouldn’t miss it.

That happened only once. She surfaced and the air pocket was a blob of water-weed. She had to swim frantically ahead until a small pocket appeared. Panic would have used too much air, so she stayed ever so calm.

It was indeed totally black—cave-black, coal-sack black—in that tunnel. Blacker than the inside of your eyelids when closed. The only light in that mile-long, days-long swim was the glow from her own wrist chronometer. A numerical firefly, it followed obediently, seeming a separate existence and not a part of her arm.

A few eons later, her outstretched right hand encountered something hard and cold. There was enough clearance so that her shoulders could rise out of the water. She held onto the grating for several seconds. Then she remembered that if certain circuits were reconnected, thousands of volts could shoot through the damp steel. She let go hurriedly. A voice sounded on her right.

“Hinges are a little stiff, Miss Kai-sung.” It was Philip. “Ah, there!”

A moment later something broke the surface on her left with a loud whoosh. It was Hammurabi. He was followed seconds later by a thin whistle: Porsupah. Even the Tolian was panting. Not because of fatigue, but because the air here was anything but fresh.