Available from The Black Library
Written by Dan Abnett
Synopsis [Spoiler alert] This bit tells you exactly what happens in the book!
338.M41, Lethe Eleven. Gregor Eisenhorn is hunting his poisoner, Beldane Sadia. Gregor is about to kill Sadia but Witchfinder Tantalid kills her first. Tantalid hates Eisenhorn because he is a psyker. Tantalid tries to kill Eisenhorn but he is saved by Meda Betancore, Midas' daughter. Midas has been killed 26 years earlier by Fayde Thuring.
Eisenhorn is summoned to Thracian Primaris to attend the victory parade to mark the end of the century long Ophidian campaign. Inquisitor Titus Endor warns Eisenhorn that Inquisitor Osma is investigating him. Eisenhorn visits Lord Inquisitor Rorken. Rorken tells him that Cherubael spared another Inquisitor's life, mistaking him for Eisenhorn and that is why he is being investigated.
Eisenhorn attends the great processional march. The victory parade is attacked. The Cardinal Palatine is killed. Ten powerful psykers escape. Ravenor, Eisenhorn’s best pupil, is crippled. Lord Commander Helican is killed. Eisenhorn tracks down one of the psykers, Esarhaddon, and Inquisitor Lyko kills him.
Eisenhorn discovers that the man Lyko killed wasn't Esarhaddon. Lyko lures Eisenhorn into a trap on Eechon, where Esarhaddon is being auctioned to the highest bidder. Eisenhorn tries to find out who Lyko is working for, but before the Inquisitor can answer he is killed by Cherubael. The daemonhost kidnaps Esarhaddon.
Eisenhorn meets up with Fischig on Cadia. He has discovered a Chaos cult worshipping Cherubael and measuring the mysterious, pre-Imperial pylons - thought to quiet the warp around Cadia. Eisenhorn discovers that the supposedly dead Inquisitor Quixos has been involved with the cult. Eisenhorn confronts the cult as they try to measure another pylon. He is attacked by another daemonhost called Prophanti. The daemonhost is destroyed but takes over the body of Husmann, one of Eisenhorn's retinue.
Inquisitor Osma arrests Eisenhorn for consorting with daemons. Eisenhorn is interrogated for three months and almost dies. With the help of his retinue, Eisenhorn escapes to Cinchare. Eisenhorn is now hunted as a fugitive by the Inquisition.
Posing as a research team, Eisenhorn and his followers discover that the skeleton crew on Cinchare are Chaos worshippers. Deep under the planet's crust, Eisenhorn hooks up with Magos Bure, an Adeptus Mechanicus Enginseer. Together they destroy the Lith, a sentient mineral suffused with the power of Chaos.
Bure has been looking after Pontius Glaw for a century. Eisenhorn promises to give Glaw a physical body in return for knowledge about daemonhosts. Bure creates unique weapons to help Eisenhorn combat the daemonhost.
Eisenhorn visits the Shrine world of Orbul Infanta to consecrate the weapons. He is attacked by Witchfinder Tantalid and is forced to kill him.
Eisenhorn tells Inquisitor Endor, Commodus Voke, Inquisitor Grumman and Inquisitor Ricci about Quixos. The Inquisitors attack Quixos on Farness Beta, supported by the Imperial Navy and the Imperial Guard. Eisenhorn destroys the body of Cherubael, unwittingly setting it's spirit free, back into the warp.
Prophanti, the second daemonhost, kills Voke. Eisenhorn obliterates Prophanti. Eisenhorn discovers Endor was forced to spy on him by Osma. Quixos kills Ricci and Grumman. Eisenhorn discovers that Quixos was trying to build copies of the Cadian pylons, amplified by powerful psykers. Eisenhorn kills Quixos.
Osma's allegations against Eisenhorn are dropped and he rejoins the Inquisition. Eisenhorn secretly creates a daemonhost to recapture the spirit of Cherubael.