Destiny and Blue pilot the International Space Agency shuttle Mercury on a mission to deploy a new satellite in Earth orbit which will identify Mysteron energy on Mars and thereby provide early warning of imminent attack. As the shuttle achieves final orbit, Destiny suddenly loses control and the Mercury becomes locked into a new flight path. Then Spectrum receives a ransom demand from an extortionist who threatens to initiate the Mercury's re-entry over North America and crash the shuttle on Washington. With a nuclear power cell on board, the consequences are unthinkable - more so if Captain Black locates the extortionist before Scarlet and obtains the shuttle's access code!