Star Trek VI :

The Undiscovered Country

Spock's protégé, Valeris, is a leading figure amongst a band of Starfleet officers who do not wish to end the formal hostilities between the Klingon Empire and the Federation.

Using her closeness to Spock and her access to the USS Enterprise, she delicately executes a plan to sabotage negotiations and maintain the status quo. As a result of her plan, Chancellor Gorkon is assassinated.

However, as always, Kirk and crew manage to defuse the situation, and for the first time in many years, peace is restored between the Klingon and Federation governments.

The title of this movie, The Undiscovered Country, refers to a Shakespearean quote which refers to death. This was a prophetic title, because this movie marked the "death" of the Captain Kirk movies, and the end of an era.