I find it hard to be objective when I review a book by Alastair Reynolds because I think it's one of the few authors with Peter F. Hamilton can write space operas. The author takes us into a world similar to ours, a century later (2150) when humans started timidly exploration and exploitation of the solar system. Operator comet located near the orbit of Jupiter, the Rockethopper vessel is diverted to Jupiter's moon Janus who just suddenly leave its orbit. Again Alastair Reynolds imagine a fascinating history. This moon "Janus" who suddenly leaves its orbit it is an artificial creation? If yes, which are the ones able to create a moon of this size, that can deal with human beings having such technological capacity? With a still superb mastery of technological explanations, based on strong personalities, the author takes us on a thrilling adventure full of twists and. One regret, however, a somewhat abrupt end and slightly caricatured but an open end which suggests a possible follow.