He departed along with the rest of his Company to investigate rumours of rebellion and uprising out on the Eastern Fringe. Unbeknownst to the Fifth, this was the precursor to the Tyranid invasion of Hive Fleet Kraken. Theodosios tried to send word back to Sotha of the threat, but his message was disrupted (presumably by the effects of the Shadow in the Warp) and merely prompted the general recall of all Scythes forces back to the home world.
When they encountered the first Hive Ship, Theodosios charged Commander Cassios with leading a diversionary attack so that his own force could destroy it. This mission was a complete failure, and the entire Company was wiped out by Tyranid resistance.
Among the other members of the Fifth Company only ever mentioned in passing recollections were Lieutenant Enero, Ancient Valtioch, Valens, Nikos, Leo, Abas, Tiberios, Messinus, and Herakleios.