The mission: board a hijacked 747 in midair. Avoid detection. Loacte and disable a hair-triggered nerve-toxin bomb that could wipe out the Easter Seaboard. Execute a split-second attack that overwhelms the terrorists and safeguards the passengers. Do it all without air-to-ground radio. And do it before an increasingly jittery U.S. military blasts the airliner out of the sky.