The Enterprise is transporting several diplomatic delegations to a conference on Babel regarding the future of the mineral-rich planet Coridan. Among the passengers are Spock’s parents, Ambassador Sarek and Amanda. There is obviously a chill between father and son owing to Spock’s choice of pursuing a career in Starfleet. Unknown to Spock or his mother is the fact that Sarek is seriously ill. There is also much tension among the delegations and a spy on board is transmitting coded messages to a ship that attacks the Enterprise. With Captain Kirk wounded in an earlier knife attack, Spock is in temporary command just as his father needs a transfusion that only he can provide.