Star Trek: The Next Generation – Allegiance [3.18]

Picard is kidnapped by an unknown assailant and locked in a mysterious prison alongside of members of several other races.  Meanwhile, he is replaced by a duplicate whose strange behavior leads the crew to eventually mutiny. 

Star Trek: The Next Generation – Yesterday’s Enterprise [3.15]

When a previous Starship Enterprise comes through a rift from the past into Picard’s time, history is changed so that the Federation has been at war with the Klingons for over 20 years.  Tasha Yar, who is alive in this timeline

Star Trek: The Next Generation – Who Watches the Watchers? [3.4]

When a member of a pre-warp civilization is injured, Dr. Crusher beams him up to sickbay, where he becomes lucid enough to see Picard, and come to believe that he is a god. 

Star Trek: The Next Generation – Shades of Gray [2.22]

When Riker is infected by a mysterious infection, the only way to stop it from killing him is to stimulate his memories.  That’s it.

Star Trek: The Next Generation – The Emissary [2.20]

The Enterprise is receives on board K’Eylehr, a half human-half Klingon envoy with whom Worf was nearly romantically involved many years prior.  She warns them of a Klingon “sleeper ship” from 75 years in the past that has just re-awakened

Star Trek: The Next Generation – The Schizoid Man [2.6]

The Enterprise responds to a distress call from the assistant to reclusive scientist Ira Graves, who is dying.  Graves is working on bridging the gap between man and machine, and secretly places his mind in Data’s body. 

Star Trek: The Next Generation – Symbiosis [1.21]

After rescuing a distressed freighter, the Enterprise become involved in a dispute between representatives of two neighboring worlds who exist in a strange symbiotic relationship. 

Star Trek: The Next Generation – Arsenal of Freedom [1.20]

The Enterprise investigates a planet of weapon manufacturers where all life has abruptly disappeared, along with an investigating Starfleet vessel.