A scientist accidentally locks herself inside a vault which is being used to store unstable matter. There is only one person who has successfully broken into a vault like this – Parker. Colonel Casey of the GDF recruits Parker for the job, but the safe cracker ends up locking himself and Lady Penelope inside as well. Virgil and Scott transport the vault to an isolated area on Thunderbird 2, where Parker and Penelope must try and free themselves and the scientist before the anti-matter explodes.
Note: This episode is a homage to the original Thunderbirds episode, Vault of Death