This series is aimed at children, but a lot of adults will watch it too, because of its Doctor Who connection. The series has moved on from the previous two years as Sarah and her team now seem established, after the initial hiccups of losing Kelsey and then Maria. Daniel Anthony's Clyde in particular is a great boost to the show, because he is likeable as well as being the 'cool kid' in contrast to Luke's slight nerd. Anthony could so easily have made his character irritating, but he gets away with it (perhaps because he's much older than the role he's playing). Clyde gets to do a voiceover at the start of the show, and this is a good introduction for new viewers or a reminder to returnees... a further intro by Sarah features some nifty CGI, which is pretty well-handled throughout the episode (with one exception, a very unrealistic explosion crater in a building just didn't look right) and the pace never lets up throughout the whole half hour.
The Rhino-headed Judoon seem like a good enemy to use from Doctor Who, because they're threatening and uncompromising. In common with stories featuring Slitheen and Sontarans, this also means this low-budget show can re-use old Doctor Who costumes and masks! But the main Judoon does seem a bit watered down here. The tough, 'shoot first and ask questions later' cops of Smith And Jones would have finished Sarah and her friends in five minutes, but this one is content to allow teenagers to cheek him, tell him what to do, and even lead him up the garden path. This could be excused because a) it's for children and b) there is an added element of comedy, but I do think they have been weakened by this story.
The plot is fun and allows the reasonably easy-to-grasp concepts of nanotechnology and body occupation to drive a good story of kidnap and pursuit, just the way a good science fiction story ought to. Sarah actress Lis Sladen gets to play herself (which she can't fail at, having done it for thirty-five years) but excels in her portrayal of her possessed self. She's a good little actress and it's a shame she didn't enjoy more success outside this one role.
As usual, Ace Bhatti and Mina Anwar provide a bit of comic relief as Rani's parents, although I can't understand why Sarah objects to her calling her just "Sarah", rather than "Sarah Jane". The Third Doctor used to call her Sarah all the time, and feel certain the fourth did on occasion too.
Nevertheless, this series opener lived up to and slightly exceeded my expectations, and I am looking forward to episode 2!