The Annals of the Heechee

by Frederik Pohl

The novel is about the multimillionaire space explorer Robinette Broadhead's efforts to solve a mystery. Even though he died in a previous novel in the series, his personality is stored on a machine. Broadhead is trying to resolve the issue of the "Assassins", which are pure-energy beings that stopped the expansion of the universe and triggered a contraction of the universe. The Assassins have concealed themselves in a black hole. Broadhead and the Heechee are trying to find the Assassins. When the Assassins come out, they converse with one of Broadhead's data-gathering computer programs. The Assassins are revealed to not be enemies.