It’s not dead, Jim: The third season roars back this week. “The Tholian Web” features a new alien menace, growing madness among the crew, a disappearing starship, and Spock and Bones at each other’s throats. “Plato’s Stepchildren” features telekinetic jocks, the first (sic) interracial kiss on television, and a singing Spock. Plus! Scotty gets drunk and wanders the corridors of the Enterprise in a kilt at least once a week.