[Icarus Athrasuriel]

Part 4

Rogal Dorn and Malcador the Sigilite, receiving the few survivors from the Dropsite Massacre, became aware of the full implications of their position. Only the Imperial Fists and Imperial Army defended Terra, and those loyal to the Emperor elsewhere were cut off and weakened. He immediately recalled all Imperial forces back to Terra in preparation for Horus' invasion.

The Sons of Horus, the Death Guard, the Emperor's Children, the World Eaters, and elements of the Word Bearers, prepared to rendezvous at Mars. The rest of the Word Bearers Legion was winning the Battle of Calth, and the Blood Angels were still embattled on Signis. The majority of the Imperial Fists' fleet was trapped in an area of the Warp becalmed by the Chaos Gods. Horus assigned the Primarch Perturabo of the Iron Warriors to engage this large force of the Imperial Fists and cripple their fleet.

At this time the Space Wolves had completed the Burning of Prospero, near the Chondax System, where the White Scars Legion was stationed. The Dark Angels were engaged in an unknown campaign on the Eastern Fringe of the galaxy. Suddenly the Alpha Legion's fleet broke from the Warp to engage the Space Wolves forces of the Primarch Leman Russ, hammering his smaller force and forcing Russ to resort to hit and run attacks. The Alpha Legion's Primarch Alpharius also attacked the nearby White Scars piecemeal in order to draw that larger, newly-reinforced Legion into the conflict, and keep them from jumping to Terra to aid in its defence.

The Primarch Jaghatai Khan desperately wished to send his White Scars Legion to aid Russ. And yet as the Traitor Legions' ships attacked, Khan received the order from the Imperial Fists' Primarch Rogal Dorn: return to Terra immediately and regardless of all other considerations. Dorn also ordered Khan to relay the order on to Leman Russ and the Space Wolves, and to add that, should Russ succeed in evading his Alpha Legion attackers, only then should he attempt the Warp jump to Terra. Relaying the message and adding his apology, the Khan and his Legion made the jump to Terra. Leman Russ shrugged, and prepared to meet the Alpha Legion with renewed determination. (With help from an unlikely quarter, the Space Wolves would eventually turn the tables on their attackers and make the Warp jump to Terra.)

As this happened, the Night Lords arrived in the Eastern Fringe of the galaxy to engage the Dark Angels, and Perturabo's armada broke Warp to engage the Imperial Fists' fleet marooned near the Chaos Space Marines' headquarters world of Istvaan V. Surviving the initial thrust of the Iron Warriors' attacks, the Fists' armada held fast and scattered Perturabo's fleet, before Rogal Dorn had his ships make their own Warp jump to Terra.
Meanwhile, in the Signis Cluster, the Blood Angels, granted new and terrible power by a mysterious mass rage (that would resurface again during the Siege of Terra) had triumphed, smashed the Chaos daemon horde they faced asunder before making the Warp jump to Terra.

Similarly at the world of Calth, the Primarch Roboute Guilliman's battered Ultramarines expeditionary force had dug in on the surface, while Roboute himself and the remnants of the Ultramarines' fleet in space began to organise hit-and-run attacks on the lumbering Word Bearers. Surveying the scene on the planet, Guilliman rapidly assessed his ground troop's positions, and began broadcasting clear, concise orders to his men, co-ordinating each pocket of defence. One such pocket, under Brother-Captain Ventanus, organised a breakout and retook Calth's defence lasguns. Ventanus' victory served to even the odds in space, buying time for the vast remainder of the Ultramarines Legion to arrive at Calth and drive off the Traitors. Now reunited, the Ultramarines finally received Malcador's orders, and immediately made the Warp jump to Terra.

As the Warmaster was moving for Terra he received an unexpected communication from the recently betrayed Thousand Sons Primarch Magnus the Red. The Space Wolves had driven the Thousand Sons from Prospero. Magnus pledged his allegiance and the allegiance of the Thousand Sons Legion to Horus and the Chaos Gods in retaliation against the Emperor for this betrayal. The Thousand Sons were en route to Terra where they would link up with Horus' forces. Of the nine remaining Loyalist Space Marines Legions, only the White Scars and Blood Angels were able to join Rogal Dorn and his Imperial Fists in the defence of Terra. Three entire Titan Legions and close to two million soldiers of the Imperial Army stood alongside them.