Written by the show’s co-producer Phil Ford, the second story in Series 4 sees the return of an old enemy. Androvax The Veil, from a race of body jumping aliens, returns to Earth in order to access the titular vault, hoping to free the last 100 of his species. Mortally ill, he realises that if he does not succeed then his race will effectively die out with him.

Despite her initial suspicions, Sarah Jane (Elisabeth Sladen) decides to help him, perhaps remembering a similar moral dilemma faced by the Doctor in Tom Baker’s ‘Genesis Of The Daleks’ story. As events spiral out of control, with Androvax capable of jumping into anyone he chooses, she is left facing the possibility that her decision could destroy the earth itself.

Beautifully paced, the two episodes speed along with barely a wasted scene. Full of members that seem to have made their way from the local trainspotting club, the local alien hunting society is rather tiresomely called the British UFO Research And Paranormal Studies Society… yes, that’s ‘BURPSS’ for short. This inevitably leads to a number of jokes along the lines of ‘pardon you’ or ‘better out than in’. This is, however, a very minor complaint in what is an excellent adventure, where the effective absence of one member seems to have had little diminishing effect on the chemistry between the members of the team.

With former Doctor Who companion Jo Grant returning and an appearance from the 11th Doctor (Matt Smith) in the next story, this series looks set to go from strength to strength.

Airs at 5.15pm on Monday 18th October 2010 and Tuesday 19th October 2010 on CBBC.