It's fine. A horror fan will probably watch it happily, but I wouldn't call it strong enough to go out of your way to watch. However it's good, solid TV. It does nothing wrong and it's playing a little with genre conventions.
The most important thing about it is that despite the subject matter, it's not racist. British TV in 1980 is sufficiently close to the seventies that I was nervous of the story becoming grotesquely offensive, but in the end they juggle their fizzing dynamite and make it look easy. It's about an African fetish doll, you see. It's got voodoo powers, except that being from Africa rather than Haiti I should be calling it "vodun". That's not so bad, but the dangerous part is that our white hero's black girlfriend is the one who likes this doll and persuades him to keep it. They call it Charlie Boy.
This could have gone in all kinds of unwatchable directions... but to my relief the episode avoided all of them. The girlfriend (Angela Bruce) is completely normal. Nothing in the story required her to be black and in fact she's far more practical and level-headed than her boyfriend (Leigh Lawson), who does things like quitting his job on a reckless assumption and driving out of blind junctions without looking to make sure it's safe. It doesn't take Lawson long to jump to supernatural conclusions, whereas there's no superstition in Bruce at all. Even her performance is thoroughly grounded. I haven't seen a more down-to-earth character in the series so far. In other words, there's nothing objectionable here and instead (given the era) it's praiseworthy in how it painstakingly avoids racism in a potentially racist story.
There is that playfulness I mentioned, though. The casting of Angela Bruce in itself is toying with the audience, while the incidental music is liable to go bizarrely loud and funky at inappropriate moments. I eventually decided that this was a homage to blaxploitation.
You wouldn't call the plot exciting, since its evil menace is a lump of wood. It never does anything. Every death has a rational explanation. The only reason to suspect Charlie Boy is the coincidence factor of these incidents all occurring one after another, which makes it possible that we're watching Lawson and Bruce go suicidally nuts. I quite like that, especially since it's surprisingly hard to sell that kind of Henry James ambiguity to a horror audience. Admittedly Charlie Boy will occasionally ooze transparent gel, but that's hardly evidence.
Surprisingly though for such a simple story, there are plot holes. Why did Bruce cut Charlie Boy's wrists, assuming that was indeed her? I don't see the rationale, except as a clumsy attempt from the scriptwriter at inducing audience paranoia. Am I wrong or did the idol get knocked over after Uncle Whatshisname fell off the roof, not before? Finally and most annoyingly, when Lawson's having trouble pulling out his knife and it breaks, why didn't he just get a pair of pliers?
The most interesting thing about the story, for me, was its Doctor Who connections. There have been plenty of Doctor Who actors in this series, but in this episode they're unusually prominent. Angela Bruce was of course Brigadier Bambera in Battlefield, but there's also Marius Goring (Theodore Maxtible in Evil of the Daleks) and a quick appearance for Jeff Rawle (Plantagenet in Frontios). There are even two Doctor Who companions! You'll have to be watching out for them, though. Janet Fielding gets her first screen role as a secretary called Mandy, while Lee Richards flashes her impressive cleavage for about three seconds and to the best of my recollection delivers no dialogue. (It's possible that I wasn't listening at that point, though.) What's that, you say? Who's Lee Richards? Why, she played Exotic Romana in Destiny of the Daleks.
For the sake of completeness I'll also mention Charles Pemberton, who was a Cyberman in Tomb of the Cybermen and an Alien Technician in episode 5 of The War Games. However if there was even the slightest chance of you knowing that, get help.
The keynote of this Hammer series is down-to-earth horror in a mundane setting, so from that point of view I'd call this episode a success. It could have been lurid and/or offensive. It's neither. I liked its Final Destination
-style teasing of the audience, with jolly foreshadowings of gruesome death. Some of these are misdirection. Some aren't. That was fun. Angela Bruce also takes her top off, although you'd need freeze-frame to decide whether or not you'd seen a nipple.
I wouldn't actually recommend this, but it's okay.