This happened just before the Summer tide, at a time when the twin planets Opal and Tecton were in orbits closest to their sun, exposed (especially for Tecton) to the action of huge tidal forces. It was to be the strongest summer tide ever to occur, which would create something that only happened once every 350,000 years. Access to unstable Tecton was formally banned, but some very persistent travelers were determined to get there.[citation needed] Professor Dari Lang, who has studied artifacts left behind by long-disappearing aliens, nicknamed the Builders, suggests she might have found the Builders herself. Luis Nanda and the Kekropian Atvar H'sial had their own interests on Tecton, and they were willing to go to any lengths to get there. And Councilman Julius Graves was hunting killers and was determined to find them even on Tecton. Planetary administrators Hans Rebke and Max Perry had no choice but to go to Tecton, risking their own lives to protect others, and perhaps learn the secret of the Summer Tide and the Builders...