An outer plasmic shell, often simply called a plasmic shell, was a TARDIS exterior. In a perfectly functioning TARDIS, the chameleon circuit picked a plasmic shell suitable to the time and place in which the ship landed. A TARDIS' shells were stored in the shell room; if the room had no suitable shells, more were created and stored as well. (PROSE: The Little Things) Lord Roche was forced to use a non-terrestrial aeroplane as his shell when he didn't have any terrestrial designs in his shell room and didn't feel like designing any. (PROSE: The Suns of Caresh) The theory in the TARDIS Handbook was that the plasmic shell was driven by the chameleon circuit. (TV: Logopolis) When a TARDIS died or was dying, its final plasmic shell might grow to enormous size due to leakage of its dimensionally