Neanderthals have developed a radically different civilization on a parallel Earth. A Neanderthal physicist, Ponter Boddit, accidentally passes from his universe into a Canadian underground research facility. Fortunately, a team of human scientists, including expert paleo-anthropologist Mary Vaughan, promptly identifies and warmly receives Ponter. Solving the language problem and much else is a mini-computer, called a Companion, implanted in the brain of every Neanderthal. But it can't help his fellow scientist back in his world, Adikor Huld, when the authorities charge Adikor with his murder.

In this Hugo-nominated novel, an alien walks into a museum and asks if he can see a paleontologist. But the arachnid ET hasn't come aboard a rowboat with the Pope and Stephen Hawking (although His Holiness does request an audience later). Landing at the Royal Ontario Museum in Toronto, the spacefarer, Hollus, asks to compare notes on mass extinctions with resident dino-scientist Thomas Jericho.

In the near future, a signal is detected coming from the Alpha Centauri system. Mysterious, unintelligible data streams in for ten years. Heather Davis, a professor in the University of Toronto psychology department, has devoted her career to deciphering the message. Her estranged husband, Kyle, is working on the development of artificial intelligence systems and new computer technology utilizing quantum effects to produce a near-infinite number of calculations simultaneously.

Experimental psychologist Jim Marchuk has developed a flawless technique for identifying the previously undetected psychopaths lurking everywhere in society. But while being cross-examined about his breakthrough in court, Jim is shocked to discover that he has lost his memories of six months of his life from 20 years previously - a dark time during which he himself committed heinous acts.

When prospector Bob Broadhead went out to Gateway on the Heechee spacecraft, he decided he would know which was the right mission to make him his fortune. Three missions later, now famous and permanently rich, Robinette Broadhead has to face what happened to him and what he is...in a journey into himself as perilous and even more horrifying than the nightmare trip through the interstellar void that he drove himself to take!