Need your help!

Hey gang. I am trying to identify a horror movie I saw when I was very, very young. It was playing on TV when I saw it and for some reason I didn't get to watch the entire film. This is a pretty vague memory but maybe y'all will remember it from my pathetic description. The movie starts with a party (maybe a seance?) at an old house. All of a sudden, the guests start dying in bizarre and grotesque ways. Some people go crazy and kill each other or there are just some very improbably accidents that bring about the party guests' demise. One person (a woman, maybe) nearly escapes, actually makes it out the front door but is struck by lightning. Cut to the next morning when the cops are there surveying the damage and taking pictures of the charred corpse by the front gate. That's all I remember. The movie struck me as either late 70s or early 80s and was either British or Canadian.

So I thought I found this one the other day in the form of Spookies but after watching that flick (which is pretty great by the way), it seems that my vague and mysterious horror movie remains vague and mysterious. Anyone who can help me figure out what the hell this movie is will get a prize (of no financial value).