Before Trills are merged, initiates are evaluated by older, more experienced Trills to determine if they are fit for merging. Dax is assigned an initiate named Arjin for evaluation and neither quite knows what to expect or how to handle the situation. Meanwhile, while flying a runabout through the wormhole, Dax and Arjin encounter a strange phenomena which they bring back to the station and later discover that it's a proto-universe which is expanding and will soon destroy the station unless they destroy it, and the possibly intelligent beings inside, first.