This was a 'monster in the house' story that turned out to be something else entirely. No one actually dies. I know. It's a rarity, right? Anyway, get ready for a lot of spoilers.
It's 1974. Professor Alec Palmer (Dougray Scott) and his assistant, psychic empath Emma Grayling (Jessica Raine of Call the Midwife fame) try to summon the ghost of a woman who haunts the mansion they're working in when there is a knock on the door. It's the Doctor and Clara, who identify themselves as "ghostbusters" sent by military intelligence to help find out what's going on. The Doctor gives away Palmer's past as a military intelligence operative, contradicting the professor's story about having been a POW in World War II. This would make more sense if actor Dougray Scott, who is forty-seven, wasn't too young to have held such a position in a war that took place over thirty years prior to the story, but for some reason writer Neil Cross felt compelled to give a nod to Third Doctor Jon Pertwee's service during WWII and didn't feel any need to get his chronology correct. Damn lazy bastard.
As things start to get weird, and then comically frightening, the Doctor and Clara take turns playing matchmaker to Alec and Emma, who have feelings for one another but are each too timid to express themselves to one another.
So basically, it's really a love story set against a haunted house. But there are some darker elements thrown in. The TARDIS, still not fully liking or trusting Clara, gets under her skin by using a holographic interface to irritate her. Clara's response: "Oh, you are a cow!" was hilarious. It was kind of creepy and funny at the same time. And when the Doctor reveals his true reason for coming to the mansion to Emma, grilling her about her impression of Clara, which turns out to be quite normal, his disbelief, his refusal to accept her for what she is, suggests hostility on his part toward his own companion, masking it in his usual friendly, buffoonish demeanor.
My favorite part came when Clara, after having witnessed Earth in its distant past, near-past, and far-flung future, practically traumatized by the weight of it all, confronts the Doctor about how he must view human beings: we're all ghosts to him, because from his perspective he's seen everyone come and go — literally.
And yet for all those smaller, brilliant moments, there were obvious flaws in the story that kept me from enjoying it as much as I did "Cold War", the preceding episode. Writer Neil Cross's bad chronology, for starters, and the lack of any real tension or fright, just didn't mesh well with the ending, and when we learn who the "ghost" is and what her relationship is to the mansion, Alec, and Emma, it all felt very contrived and fake. "Hide" is only slightly better than Cross's other episode script, "The Rings of Ahkaten", but that's not really saying much in its favor.