In the aftermath of the Fall of Sotha and the Chapter's subsequent losses against the Tyranids of Hive Fleet Kraken, the Scythes of the Emperor set up outposts on a number of planets that were staffed by Apothecaries and medicae serfs; these outposts were to conduct gene-screens of the populations of the chosen worlds, in the hopes of finding suitable candidates to recruit as new Aspirants for the Chapter. Aratus was stationed in an outpost located in the city of Tamuero on Brakur IV.
When the Tyranids invaded the Brakur System, it was decided to evacuate the outpost in order to preserve the Chapter's gene-seed stocks. Sergeant Cassander led his Assault Squad deployed from the Strike Cruiser Atreides in an extraction mission to get Aratus and the gene-seed offworld. However, the squad's Storm Eagle was attacked and destroyed by a Harridan with only two survivors: Esau and Galerius.
Esau and Galerius were able to complete the drop into Tamuero. Initially intending to extract Aratus alone, the Apothecary convinced them to save his attendant medicae-serfs as well. Using an Onager lighter, the Marines and the serfs were able to escape Brakur IV. The battle for the Brakur System itself continued to rage, however, and it is not known whether the Scythes were able to rescue the gene-seed.