In an alternative London of the 1890s where computer technology is prevalent, Sebastian O escapes from an insane asylum to exact vengeance on the people who put him away.
When a bombing at a Promenade restaurant injuries members of different races, Odo is under pressure to find the perpetrator to prevent a diplomatic incident.
With Kahless and the Red Path in possession of the destructive power of the Crystalline Entities, Worf decides that they need someone who understands the Crystalline Entities...