Sarah Jane and the gang face some old alien enemies again, along with an altogether unexpected foe, in the final two-part adventure of the series.

A news report on a couple looking for their missing son, Ashley, brings a surprise for Sarah Jane when she discovers that the missing boy looks exactly like Luke. And when Mr Smith, Sarah Jane's super-computer, confirms that Luke is a genetic match with Ashley, Sarah Jane sends him back to live with his "parents".

Source: BBC