A news report on a couple looking for their missing son, Ashley, brings a surprise for Sarah Jane (Elisabeth Sladen) when she discovers that the missing boy looks exactly like Luke (Tommy Knight). And when Mr Smith (Alexander Armstrong) confirms that Luke is a genetic match with Ashley, Sarah Jane sends him back to live with his ‘parents’. With no knowledge of his former life, Luke finds it hard to fit in and, when he tries to escape, he makes a startling discovery about who his parents really are. Sarah Jane, meanwhile, makes some investigations into the Pharos Para-Science Institute – a research unit that has been conducting experiments using alien technology. Floella Benjamin guest stars as Professor Rivers.