Changes

The story follows [[Warmaster]] [[Horus]] has fallen to [[Chaos]], but his plans of rebellion against the individual stories [[Emperor]] are known only to a few he trusts to side with him. [[Primarchs|Primarch]] [[Angron]], [[Mortarion]] and [[Fulgrim]] of the main loyalist leaders [[World Eaters]], [[Death Guard]] and [[Emperor's Children]] respectively have all sided with Horus and their four Legions gather in the Isstvan system on Isstvan IIIthe pretence of crushing a rebellion by the Isstvanians. The unconscious [[Euphrati Keeler]] has developed a cult following who believe the [[Emperor]] is a deity and she is a saint, [[Kyril Sindermann]] chief among them. The group gets word that forces loyal to Horus are coming to kill her and [[Titus Cassar]]- of the Legio Mortis [[ModeratiTitan]] of the Legion begs his friend [[ImperatorJonah Aruken]] to help him save her. Aruken grudgingly agrees and he, Cassar and Sindermann go to rescue Keeler, only to find Maggard, former bodyguard of remembrancer [[TitanPetronella Vivar]] but now genetically-enhanced enforcer for Horus about to kill her. Maggard attacks them but becomes unable to move, the bullets from his gun moving very slowly, and the three men realize that Keeler has awoken and is using her powers to save herself and them. Before Maggard can stop them they carry Keeler to safety amidst the bowels of the Vengeful Spirit''s lower decks.  The assault force that will descend to the surface of Isstvan III to persecute the war is chosen squad-by-squad, which is unorthodox, piquing the suspicion of [[Dies IraeSaul Tarvitz]]of the Emperor's Children. Tarvitz talks his way into remaining in the fleet when the assault force deploys and on the gun decks discovers the ship's crew loading lethal Virus Bombs into the ship's weapons. Realizing that the Space Marines deployed to the surface are about to be betrayed and wiped out, Tarvitz steals a [[AstartesThunderhawk]] and flies for the surface to warn them. He is pursued by members of his own Legion who are part of the betrayal and in desperation communicates with [[Space Marine Captain|Nathaniel Garro]], Battle-Captainof the Death Guard 7th Great Company who is stuck in-fleet after losing a leg in a preliminary engagement against the rebel Isstvanians. Garro, an old friend of Tarvitz's, believes him when he tells him of the imminent betrayal and orders his friagte Eisenstein to fire on the Thunderhawks pursuing Tarvitz. The resulting cloud of debris hides Tarvitz from the fleet's sensors as he lands on Isstvan and Garro reports that Tarvitz is dead before preparing to jump to the [[Warp]] and bring warning of Horus's betrayal to the [[Garviel LokenEmperor]] leader .  Meanwhile on the surface those Space Marines of the [[Sons of Horus]] 10th Company, World Eaters, Emperor's Children and Death Guard whom their primarchs deemed to loyal to the Emperor to rebel against him battle the rebel Isstvanians, the Sons of Horus and Emperor's Children led by [[Garviel Loken]], [[Tarik Torgaddon]] and [[Lucius]] taking the enemy stronghold. Saul Tarvitzarrives and warns them of their imminent betrayal and most of them are able to take shelter before the Virus Bombs fall. Crewing a Titan on the surface Jonah Aruken and Titus Cassar hear the command to power down and seal their machine, their Princeps being loyal to Horus and so having received warning. Cassar realizes what is happening and tries to sabotage the Titan, pleading with Aruken to help him, but Aruken chooses ambition over loyalty and shoots Cassar dead. In the fleet Horus gathers the remembrancers attached to the four Legions and shows them the bombing before ordering his men to open fire, massacring them. [[Kyril Sindermann]] and [[Mersadie Oliton]] escape alongside [[Euphrati Keeler]] when she leads them to [[Iacton Qruze]] , an elderly Captain of the Sons of Horus, who leads them away from the [[massacre. The four arrive at the Vengeful Spirit's hangar and plan to steal a Thunderhawk but are intercepted by Maggard. Qruze and Maggard fight but are evenly matched until Kyril Sindermann picks up a blade and stabs Maggard in the side, allowing Qruze to finish him off. The four steal a Thunderhawk and flee, guided by Keeler to the Eisenstein where Nathaniel Garro takes them aboard.  Infuriated by the survival of the loyalists on the surface Angron spearheads a World's Eaters attack wave to destroy them without waiting for Horus's orders. Forced to support him Horus deploys the traitor Sons of Horus, Emperor's Children and Death Guard, turning what was meant to be a single wipeout blow from orbit into a protracted ground war. Saul Tarvitz emerges as a brilliant leader, commanding the loyalists as they repel wave after wave of traitor attacks while slowly being whittled down. Frustrated and jealous that Tarvitz is getting all the glory Lucius slays traitor Emperor's Children[[Chaplain]] Charmosian and uses his helmet microphone to contact the traitors, selling out the loyalists in exchange for a place in his traitor Legion . Lord Commander [[Eidolon]] launches a devastating attack that hits the rebels where they are vulnerable, acting on Lucius's information, while Lucius slips away and Garviel Loken and Tarik Torgaddon go to confront their traitorous former [[Mournival]] brothers [[Ezekyle Abaddon]] and [[Horus Aximand]]. The confrontation splits into two duels as Loken fights Abaddon and Torgaddon fights Aximand. Aximand kills Torgaddon, leaving Loken helpless against Abaddon who all have to deal with the unthinkable treachery of grievously wounds him before the building they are fighting in is destroyed by a traitor [[WarmasterTitan]] . The traitor forces pull back, the rebels all but destroyed, and Horusorders the fleet to firebomb the planet from orbit, scouring it of all remaining life.