Available from The Black Library
Written by Dan Abnett
Synopsis [Spoiler alert] This bit tells you exactly what happens in the book!
The Inquisitor Gregor Eisenhorn and his retinue, including Midas Betancore (a pilot) and Uber Aemos (a savant), arrives on Hubris, hunting Murdin Eyclone.
The population of Hubris is hibernating, waiting for the planet to spin closer to it's sun. Eisenhorn discovers Eyclone has connected Hubris' cryogenerators to a casket, but it's contents are missing. Eisenhorn kills Eyclone.
The Governor of Hubris allows Eisenhorn to carry on his investigations on the condition that he is accompanied by Godwyn Fischig of the Adeptus Arbites. During his investigations, Eisenhorn encounters Alizebeth Bequin, a drifting prostitute. He offers her a place in his retinue because she is an untouchable - immune to psychic powers. Eisenhorn discovers a link between Eyclone and the noble Glaw family of Gudrun.
Eisenhorn commissions Tobius Maxilla, owner of the sprint trader Essene, to take him to Gudrun. The Essene is boarded for inspection upon arrival by a fake Navy detail. Eisenhorn foils the attack but, with the aid of Olm Madorthene of the real Imperial Navy, pretends the assassination attempt has been successful.
Eisenhorn joins forces with Commodus Voke, another Inquisitor investigating the Glaws. Posing as a grain merchant, Eisenhorn organises a meeting with the Glaws on their massive estate. He discovers that the contents of the casket - the Pontius - are of secondary importance compared to the 'true matter' which involves the Saruthi, a Xenos race.
Eisenhorn is discovered and then tortured by Gorgone Locke, a ship master in the pay of the Glaws. Eisenhorn escapes a pit fight and, with the help of Voke, destroys the Glaw household. Several key individuals escape, though, including the Ecclesiarch Dazzo, Locke and Oberon Glaw. More Inquisitors become involved in the investigation, including the radical Molitor.
Eisenhorn goes to the planet of Damask, where the Glaws have been mining Xenos artifacts, and finds they have been consorting with traitor Marines of the Emperor's Children Legion in the shape of Mandragore. Eisenhorn steals the Pontius, which fits into the casket from Hubris. The Pontius is the preserved intellect of Pontius Glaw, a noble from house Glaw who 'died' several centuries ago. Eisenhorn interrogates Pontius and discovers the 'true matter' is the Necroteuch, a powerful book revealing the secrets of Chaos. The Saruthi have a copy, and are willing to trade it for their recovered artifacts.
Eisenhorn follows the Glaws into the strange dimensions of Saruthi space. There, he allies with Gudrunite Guardsmen deserting the Glaws, and attacks as the exchange is taking place. Eisenhorn kills Mandragore and destroys the Necroteuch. Oberon Glaw is killed in the battle. Malahite (the Glaws archeoxenologist) is captured. Ecclesiarch Dazzo and Gorgone Locke escape again.
Eisenhorn reports back to the Inquisition. Malahite is tortured and killed by Molitor before Eisenhorn can question him. Eisenhorn and Voke perform an auto-seance to interrogate Malahite's soul in the warp. He tells them that the Saruthi made a copy of the Necroteuch.
Eisenhorn follows Locke and Dazzo back to the Saruthi homeworld at the head of an invasion force. Eisenhorn finds the dying Dazzo who has recovered a translation tool for the Saruthi version of the Necroteuch and passed it on to Locke. Eisenhorn kills Locke and takes the translation tool. Molitor attacks Eisenhorn for the tool. Eisenhorn kills Molitor. Cherubael, a daemonhost created by Molitor, demands Eisenhorn give him the translation tool. Eisenhorn destroys it.
The daemonhost and Eisenhorn escape the Saruthi planet before it and the Necroteuch is obliterated.