Renegade Rocket
The Mysterons threaten to, and launch a nuclear device that will devastate an unspecified target once it reaches its destination.
The source of the missile is quickly traced, but the four letter password that will allow them to activate the self destruct on the missile has been taken by the Mysteron agent. Whilst the Angels attempt to track down the renegade agent, Blue and Scarlet track down the target of the missile. Because it does not show up on any radar scanners, they realise that the course has taken it directly vertical, and the downwards course will be identical.
A race against time is compounded by the agent's suicide before the Angels can reclaim the missile controller that had the password stored on it. The device sinks to the bottom of the sea, where rip currents batter it.
Scarlet and Blue defy orders by remaining after the base has been evacuated to attempt the remote destruction of the rocket. They are working down an alphabetical list, and reach AMEN in the time that they have left. This fails, but the rocket explodes anyway. Assuming that they have succeeded, they appear smugly before Colonel White, who reveals the real reason for the destruction of the rocket - the original controller had toppled and landed on the "Self-Destruct" button, and that the codeword had, in fact, been ZERO. However, he lets them off the hook.