The Tyrryxians sent their battle fleet in pursuit of the Mantis, but one of the ship's devices could shrink or enlarge the ship or any object aboard it. They used it to shrink themselves to particulate size to avoid detection, but while they were still in giant mode, the Doctor's TARDIS materialised on board. The Mantis leader discovered the TARDIS and experimented on it to find out what it was, subjecting it to acid and x-rays. Learning that it was a dimensionally transcendental craft, he forced the Third Doctor out and demanded that he reveal his scientific secrets. The Doctor escaped, made contact with miniaturised Tyrryxians, and they worked together to get the leader on board the TARDIS and then re-enlarge it, destroying the stolen spacecraft. The leader was miniaturised and imprisone