“Thanks, guys.” Rebka crumpled the message into a ball and threw it over his shoulder. “He’s crazy and he can do anything he likes — but it’s my job to control him and stop him. And if I don’t, my head rolls! Just perfect.”

It was another fine example of action at a distance, of government trying to control events a hundred light-years away. Rebka set to work on the next message.

That took another hour. It did not seem much use when he had it, but at least it provided information and did not ask for outright impossibilities.

…PERHAPS OF NO DIRECT RELEVANCE TO YOUR SITUATION, BUT THERE ARE WIDESPREAD AND INDEPENDENT REPORTS OF CHANGES IN BUILDER ARTIFACTS THROUGH THE WHOLE OF THE SPIRAL ARM. STRUCTURES THAT HAVE BEEN STABLE AND INVARIANT THROUGHOUT HUMAN AND CECROPIAN MEMORY AND IN ALL REMAINING ZARDALU RECORDS ARE EXHIBITING FUNCTIONAL ODDITIES AND MODIFIED PHYSICAL PROPERTIES. THIS IS ENCOURAGING MANY EXPLORATION TEAMS TO REEXAMINE THE POSSIBILITY OF PROBING THE UNKNOWN INTERIORS OF A NUMBER OF ARTIFACTS…

“Tell me about it!” Rebka glared at the computer that was displaying the offending transcript. “And don’t you remember that I was all set to explore Paradox, before this idiot assignment? Before you dummies pulled me away!”

…WHILE PERFORMING YOUR OTHER DUTIES YOU SHOULD OBSERVE CLOSELY THE ARTIFACT OF THE DOBELLE SYSTEM KNOWN AS THE UMBILICAL, AND DETERMINE IF THERE HAVE BEEN SIGNIFICANT CHANGES IN ITS FUNCTION OR APPEARANCE. NONE HAVE SO FAR BEEN REPORTED…

Rebka turned to stare back the way he had come. The Umbilical was long since invisible. All he could see was a broken line on the planet’s terminator, like a glowing string of orange beads on the curving horizon. A major eruption had begun there. He looked down to the surface over which he was flying — all quiet below — and skipped to the third message.

Which made up for the other two. It was the answer to Rebka’s own query.

…A CECROPIAN ANSWERING YOUR DESCRIPTION. SHE IS INTERESTED IN LIFE-FORM EVOLUTION UNDER ENVIRONMENTAL PRESSURE, AS YOU SUGGEST, BUT SHE IS ALSO KNOWN AS A SPECIALIST IN BUILDER TECHNOLOGY…

…SHE GOES UNDER A VARIETY OF NAMES (AGTIN H’RIF, ARIOJ H’MINEA, ATVAT H’SIAR, AGHAR H’SIMI) AND CHANGES OF EXTERNAL APPEARANCE. SHE MAY BE RECOGNIZABLE BY AN ACCOMPANYING SLAVE INTERPRETER OF THE LO’TFIAN FAMILY. SHE IS DANGEROUS TO BOTH HUMANS AND CECROPIANS, RESPONSIBLE FOR AT LEAST TWELVE DEATHS OF KNOWN INTELLIGENCES AND TWENTY-SEVEN DEATHS OF PROBATED INTELLIGENCE.

ADDED NOTE: LOUIS NENDA (HUMAN, REPUTED AUGMENTATION), FROM KARELIA IN THE ZARDALU COMMUNION, IS ALSO HEADED FOR DOBELLE. HE IS ACCOMPANIED BY A HYMENOPT SLAVE. NO DETAILS ARE AVAILABLE, BUT THE KARELIA NET SUGGESTS THAT NENDA MAY ALSO BE DANGEROUS.

NEITHER THE CECROPIAN NOR THE KARELIAN SHOULD BE ADMITTED TO THE DOBELLE SYSTEM…

Rebka did not throw the printout from the car — it was moving too high and too fast for that. But he did crumple the message and toss it over his shoulder to join the other two. He had spent more than three hours deciphering those missives from Circle headquarters, and all they offered was bad news.

He lifted his head and stared out of the window ahead. Amaranth was behind him, and the car’s roof shielded its light. He looked west, ready to catch the last gleam of Mandel-set before the primary was lost behind the dark crescent of Quake. The sun’s rim dipped below the horizon.

His eyes adjusted. And as they did so they picked up a faint, blinking light flashing from a tiny red bead next to the control console. At the same moment an insistent beep started within the cabin.

Distress circuit.

The skin on the back of his neck prickled with anticipation. Sixty hours to Summertide. And someone or something, down on the looming dark surface of Quake ahead of him, was in big trouble.

The line of the beacon would bring him down on the fringes of the Thousand Lakes area, not far from the region Max Perry favored for the location of the Carmel twins. Rebka checked the car’s power supply. It was ample — each aircar could make a trip right around Quake and still have something in reserve. No reason for worry there. He sent a brief message to Perry and Graves, then increased the car’s speed and set his new course without waiting for either acknowledgment or approval.

Mandel was still hidden, but Gargantua was high in the sky and providing enough light to land by. Rebka stared ahead. He was skimming low over a chain of circular lakes, waters steaming and churning. Their turbulent surfaces matched his own mood. Nowhere, from horizon to bleak horizon, was there a sign of life. For that, he would have to look into the waters of the Thousand Lakes themselves, or in the deepest hollows of the Pentacline Depression. Or deeper yet — the most tenacious life-forms would burrow far under Quake’s shifting surface. Would the Carmel twins have had the sense to do the same?

But maybe he was already too late. The twins were no specialists in harsh-environment survival, and every second the tidal forces at work on the planet below him grew bigger.

Rebka increased speed again, pushing the car to its limits. There was nothing else he could do. His mind wandered away into troubled speculation.

Gravity is the weakest force in nature. The strong interaction, the electromagnetic interaction, even the “weak” interaction that governs beta decay, are many orders of magnitude more powerful. Two electrons, one hundred light-years apart, repel each other with an electric force as great as the attractive gravitational force of two electrons half a millimeter apart.

But consider the gravitational tidal force. That is weaker yet. It is caused only by a difference of gravitational forces, the difference in the pull on one side of a body from the pull on the other. While gravity is governed by an inverse square law — twice the distance, a quarter the force — gravity tides are governed by an inverse cube law. Twice the distance, one eighth the force; thrice the distance, one twenty-seventh the force.

Gravity tides should be negligible.

But they are not. They grip a billion moons around the galaxy, forcing them to present the same face always to their master planets; tides worry endlessly at a world’s interior, squeezing and pulling, releasing geological stresses and changing the figure of the planet with every tidal cycle; and they rip and rend any object that falls into a black hole, so that, no matter how strong the intruder may be, the tides will tear it down to its finest subatomic components.

For that inverse-cube distance relationship can easily be inverted: one half the distance, eight times the tidal force; one third the distance, twenty-seven times the tidal force; one tenth the distance…

At closest approach to Mandel, the Dobelle system was one eleventh of its mean distance from the primary. One thousand three hundred and thirty-one times the mean tidal force was exerted upon its components.

That was Summertide.

Hans Rebka had been told those basic facts by Max Perry, and he thought of them as he overflew the surface of Quake. Every four hours, the vast invisible hand of Mandel and Amaranth’s gravity squeezed and pulled at Opal and Quake, trying to turn their near-spherical shapes into longer ellipsoids. And close to Summertide, tidal energy equivalent to a dozen full-scale nuclear wars was pumped into the system — not just once, but twice every Dobelle day.

Rebka had visited worlds where global nuclear war had recently taken place. Based on that experience he expected to see a planet whose whole surface was in turmoil, a seething chaos where the existence of life was impossible.

It was not happening. And he was baffled.