Doctor Who's new assistant Donna is in for a surprise when she visits her first alien world.
The Ood were last seen falling into a black hole a couple of series ago - but they're back on the TV in this series' third episode.
And on the planet Ood-Sphere, the pair (played by David Tennant and Catherine Tate) discover terrible truths about the human race.
Chief writer Russell T Davies says: "Donna is certainly in for a shock."
The show, called Planet of the Ood, sees the aliens - who use a globe translator gadget to speak - being used as slaves.
But a secret buried for 200 years threatens to rise up and engulf them all.
Russell T Davies added: "We're delighted The Ood are making a welcome return to Doctor Who.
"They were last seen falling into a black hole back in series two and we think it's only fair for the viewers to find out what the Ood have to say for themselves!"