Mr. Spock leads the Federation party as they travel by shuttle through the rift just as a group of the aliens arrive in Federation space. The meetings go smoothly until the Calligar take Spock's party hostage and Kirk discovers that the aliens are keeping a deadly secret. With angry Tellarite and Andorain fleets ready to attack the Calligar, Kirk must save Spock and the others before war breaks out and the rift closes for another fifty years.