In which Rani Chandra and Clyde Langer wake up one morning to discover that they appear to be the only people on Earth.
The previous night at Sarah Jane Smith's house, Mr Smith had been monitoring strange signals emanating from space. Initially, they notice that their families have vanished, but when they take to the streets they find that the disappearances cover the whole area. TV and radio channels show only static. They move towards the centre of London, discovering that the disappearances are ever more widespread. When they decide to head back to Sarah's home they hear a noise, and spot a boy in school uniform. They pursue him and are led to a tower block where the boy lives. His name is Gavin and he tells them that he is an orphan, living here with a foster family, of whom he has had many. He seems scared of Clyde and Rani, rather than happy to see other people.
A strange noise is heard and Gavin runs off. Clyde and Rani look for him, but stop at a cafe to get some food. They hear the noise again, and a message comes over the TV, radio and their mobile phones - a voice demanding the sun and the air. Going outside they split up to look for Gavin, but both encounter giant robots - one red and the other yellow...
Gavin reappears and saves Rani, whilst Clyde also manages to evade his robot attacker. They go back to the cafe where Sarah's friends start to reminisce about their life since encountering Sarah Jane Smith. This leads them to realise something which makes them different from everyone else they know. At the conclusion of their encounter with the Judoon, they had been grounded - forbidden from leaving the Earth. This might explain why they have not been taken, but not Gavin, who claims to know nothing of aliens.
The robots burst in and corner Clyde and Rani, whilst Gavin slips away. The robots scan them, but don't harm them. They reiterate their demand for the sun and air.
However, it soon becomes apparent that what they are really looking for is the son and heir. Gavin is really an alien prince, who was sent to Earth as a baby for safety when his planet was attacked. The threat is now gone, and the robots have been sent to bring him home. Recalling Gavin's love of nature, they trace him to a local wildlife park, bringing the robots with them. However, the machines can't see him. He is wearing a bio-damper which was given to him to protect him. They convince him to remove it, and the robots tell him of his true nature, and show him images of the planet he is to rule. He agrees to go with the robots, knighting Clyde and Rani before ordering the robots to return the Earth's population.
Back on Bannerman Road they tell Sarah and Mr Smith of everything that has happened, as no-one knows they have gone anywhere apart from some lost time. Their solo adventure has brought the pair closer together.
The Empty Planet was written by Gareth Roberts, and was first broadcast November 1st and 2nd, 2010.
The story is very much a character piece for Anjli Mohindra as Rani, and Daniel Anthony as Clyde, as every scene features one or both of them. It also starts to develop their personal relationship with each other - hinting at a blossoming romance. Had the series not ended prematurely the following year, this romance would have been developed further by the production team.
Lis Sladen only features briefly at the beginning of the first episode, and the end of the second - making it a Sarah-lite story, much as Mark of the Berserker had been in Series 2, and Mona Lisa's Revenge in Series 3.
The only other cast member of note is Joe Mason, who plays Gavin, though we also briefly see Rani's parents, and Clyde's mum Carla (Jocelyn Jee Esien), who has featured only a couple of times in the series.
The story is also notable for the extensive location footage, with very little studio work.
Overall, quite a nice little episode. The first section sets up the mystery very well, and you're really intrigued to know what has happened to everyone - and why Clyde and Rani haven't been affected. It's the nature of the series that the resolution is going to be a little bit twee, but it is still good to see Clyde and Rani get so much screen time. A special mention must be made of the excellent robot designs as well.
Believe it or not, but there are no things you might like to know about this story. Lots of little continuity references, but that's your lot.