Romana is in danger again, banished by Vivien, and The Doctor and Emilia have discovered Vivien is the Cailleach. One of the stone creatures, an Ogri sets in pursuit of them, but the Doctor outsmarts it. The Doctor discovers that Romana is trapped in the same location but in a different time, in hyper space, and with Emilia and K-9's help creates a device for reaching there. They succeed and the Doctor is sent into Hyper Space, but waiting there is the Caileach..... K-9 is protecting Emilia from the Ogri, but they must re-charge with blood. The Doctor discovers the vessel was a convict ship and unwittingly releases The Megara. Vivien attempts to bring back the Doctor but instead returns Vivien who destroys the machine and the only means of escape for Romana and The Doctor......
Tom and Beatrix are a joy to watch together, they are so much fun, I'll say again she'd have made a superb companion.
The Hyper Space ship is well realised and is an imaginative idea.
Part 3 is till good, but is slightly down on the quality of Parts 1 and 2. Hammer Horror is joined by real 70's sci fi. Maybe the reveal of Vivien Fay was premature, perhaps it should have been delayed until the third Part.
The scene of The Ogri killing the couple camping is truly disturbing and is genuinely the stuff of nightmares, the red flash out is very late night horror. I'm surprised they got away with it.
Overall it's a very good episode with some wonderfully scary moments.