Tau invasion confirmed on Tyranteous

Throughout much of 012M42 the Imperium had been dealing with a number of serious threats in the Zadoc subsector. Alexander's ambitious plans to secure the Rim Worlds and secure Grimlock had gone horribly awry, seeing his departure as overall commander of the subsector. His replacement, Brooke, was a more defensive minded character and his priorities had been to fortify the Imperial position on Zadoc and in the Mabb Nebula in preparation for an obvious tyranid attack, and the war against the orks on Hylas.

Defensive preparations had been going well, and the uprising on Tyranteous had been quarantined. Hollyden was cordonned off and the island of Hollydale had been cleansed. For now it seemed that despite setbacks against the orks, and Veers' disastrous attempt to land on Grimlock, the subsector, or at least what was left of it, was well prepared to meet the threat that hive fleet Nemesis surely posed.

Since the fall of Tyndareous the Imperial planners had been content to ignore the Tau. With their extended supply lines and facing enemies themselves in the Aleph expansion sphere, it looked unlikely that another major war would erupt between the Imperium and the Tau Empire at least for the time being. There had even been attempts to secure an alliance against Nemesis during 012M42, but these talks had largely fallen through.

Until late on in the year, probing attacks by the Tau in the Tyranteous system had been largely dismissed as isolated raids by an overly aggressive faction of the alien race, but during 12.012M42 it became apparent that the Tau had a base somewhere in the system, and had begun landing forces on Tyranteous itself. General Mikell Denham conferred with the Imperial governor, Diana Selken, and agreed to divert three regiments of Librian guard to the frozen northern wastelands to "monitor events". On 1712.012M42 Denham lost contact with one northern outpost, and later in the month units in the north reported a strong offensive by several tau hunter cadres moving south in the snow.

Initially the imperial command was keen to dismiss the reports as over-reactions, but the Librians soon came under strong attack from tau forces from at least two sept worlds. This wasn't a probing attack, this was an invasion! The Librians attempted to put up a stubborn defence, but railgun fire made scrap metal of their armoured units early on, and a counter attack led by Librian mechanised units failed to blunt the tau advance. Stealth suits managed to infiltrate into the Librian defensive positions, and by the end of 012M42, the entire line was falling back.

Unexpected help arrived in the nick of time as it appeared the breach in the imperial lines would lead to disaster. Such was the pace of the tau advance that the Librian regiments became separated and isolated, and the road to Fallowvale lay wide open. Before the tau could exploit the situation however, a company of Apocalypse Riders astartes made planetfall just north of the threatened imperial settlement. The astartes force, largely made up of fast moving bikes and land speeders, had intercepted General Denham's communications to his hard pressed front line commanders on their way to Hylas, and made a diversion. The Apocalypse Riders decided to attach one company of their force to the Zadoc subsector, and another to the Perseus Deeps, operating as a rapid reaction strike force.

The astartes immediately counter attacked the tau, making lightning raids against the aliens but never staying long enough for the enemy to mount an effective counter-attack against their small force. Wherever the marines appeared, the tau assault was stopped in its tracks, and this allowed the imperial generals to regroup their battered formations into a semblance of a stable front line. The three Librian regiments were saved from absolute destruction and Denham reinforced the line with hastily raised PDF divisions. The Riders, their job done, re-embarked on their strike cruiser and headed into the Mabb Nebula.