|Behind the scenes|
Eslin 359 was assigned to a human named Gary Kozlar due to his position at the the observatory. However, his poolmate Derane 344 - to whom Eslin had become close - was assigned to a minor post. When the Animorphs destroyed the Earth-based Kandrona, the Yeerks were forced to shuttle their people to the orbiting Pool ship in order to feed them, and due to a lack of resources, not all Yeerks were able to be kept alive in this manner. While Eslin was given priority due to his position, Derane was deemed expendable, and died of Kandrona starvation.
Heartbroken, Eslin plotted revenge against Visser Three, whom he blamed for Derane's death. He sabotaged one of the Yeerk shuttles, throwing off the feeding schedule and causing Controllers to collapse in plain sight of uninfested humans as their Yeerks died. But his true goal was to kill Visser Three himself. Mindful that he alone could not accomplish this feat, he enlisted the help of Aximili-Esgarrouth-Isthill, who had accidentally uploaded advanced Andalite software to the observatory's computers and was attempting to remove it.
Eslin reminded Ax that Visser Three fed as an Andalite would, in order to keep his host body, Alloran-Semitur-Corrass sustained. He informed Ax of the location at which the Visser would next be feeding, trusting that the Andalite would attack Visser Three in order to avenge his brother's death. Ax did indeed ambush and attack Visser Three, but was unable to kill him.
Ax later returned to the observatory, and forced Eslin to set up the Z-space communication link with the Andalite homeworld just one last time and then would he would be out of Eslin's life, citing that if he refused, Ax would find a way to inform Visser Three of Eslin's betrayal. Eslin reluctantly complied.