In case you skip it...

In this episode, it’s finally learned what happened to the Seleya, the Vulcan ship that was lost in the Delphic Expanse, and also by implication what happened to the Vannkara, the ship sent after it.

Enterprise comes across the Seleya adrift in an asteroid field rich in trellium ore. They had been gathering trellium ore to protect their ship against the Expanse’s spatial anomalies, but it turned out that trellium is a powerful neurotoxin for Vulcans. Exposure to it destroys the neural pathways involved in emotional control, causing paranoia, then aggression, then violence and insanity.

T’Pol is briefly exposed and loses some emotional control, but is treated and expected to recover fully. The crew of the Seleya are too far gone and cannot be rescued or cured.

Enterprise harvests enough trellium ore to insulate their forward hull, but doing so would result in T’Pol’s death. Archer orders the ore to be kept in a biohazard locker in the cargo bay until Phlox can find a way to inoculate T’Pol from its effects.