Terror of the Zygons. Tom Baker's Doctor, what Sarah impressed Rose with in School Reunion. Nessie is (SPOILERS ...) a cyborg essential to the survival of a race who crash-landed on Earth and subsequently discover their planet has blown up so they need a new one. And yes, the Brig decided to wear his regimental tartan leading to desperate attempts to keep a straight face on the part of his colleagues.

Er, my era, all right? :)