Star Trek: The Next Generation – Unification I [5.7]

Picard is informed that the famed Ambassador Spock has abruptly and mysteriously left Vulcan to go to Romulus.  Concerned that he may have defected, Picard and Data go after him. 

Star Trek: The Next Generation – Sarek [3.23]

The Enterprise plays host to important negotiations that can only be held by legendary Federation ambassador Sarek.  However, the aged Sarek is suffering from a rare debilitating disease that causes his emotional control to break down.