Straker's son John lives with Straker's ex-wife Mary, who has re-married. Straker is having a day out with the boy, John, but it ends in an argument with Mary and John is run over and seriously hurt. Drugs can be obtained to save him in America and a SHADO craft is sent to fetch them. However, Straker gets an alert call to say that an alien defector which could do untold damage to Earth is in the range of the SHADO craft. SHADO can destroy the alien but it means diverting the means to save John.
—don @ minifie-1