Saru returns to help the U.S.S. Discovery uncover the mystery of an unusually destructive new force. As Burnham leads the crew, she must also find a way to help Book cope with an unimaginable loss.

Tilly and Adira lead a team of Starfleet Academy cadets on a training mission that takes a dangerous turn. Meanwhile, Burnham is pulled into tense negotiations on Ni'Var.