ST:TNG:28 - "Where Silence Has Lease" (Stardate: 42193.6) - this is an interesting episode - the Enterprise encounters an entity that is devoid of matter or energy - essentially it is nothing. Once the Enterprise is pulled into the entity so it can learn about Picard and crew, about death, they decide to do the unthinkable - self-destruction. As a trivia note, originally the producers wanted Richard Mulligan (of the series "Empty Nest") but he wasn't available - but as an homage, they named the entity in this episode as Nagilum (Muligan backwards!). We also see another Galaxy class starship, the Yamato, as well as an homage to Jerry Goldsmith's Klingon Theme at the beginning of the episode when Worf shares his Klingon calisthenics program with Riker you get to see Worf's Klingon instincts (such as anger) again here.
Review of Where Silence Has Lease
