What you are about to unleash is evil, unspeakable evil.
Even outside of their work for Hammer Films, producers often sought to pair up Peter Cushing and Christopher Lee. That was certainly the case with 1973's The Creeping Flesh, which was directed by Hammer vet Freddie Francis. In it, Cushing plays a professor who returns from New Guinea at the end of the 19th century with the oversize skeleton of a primitive man in tow. What's especially strange about it is the way it grows living flesh whenever it's exposed to water, and its blood has a deleterious effect on anyone it's injected into, as Cushing learns to his chagrin when he tries out a serum derived from it on his sheltered daughter (Lorna Heilbron). The ironic thing about it is he was worried that she would turn out as batty as her mother, who died in an insane asylum, and his actions actually turn this fear into a reality.
Meanwhile, Lee co-stars as Cushing's half-brother, whose mental institution gives him the human guinea pigs he needs to conduct his research into the human mind and its susceptibility to slipping into madness. Alternately, he could have just waited for the next family reunion to come around. As it is, the film creeps along at its own pace, but it kicks into high gear when Lee takes it upon himself to relieve Cushing of his skeleton on a stormy night. Surprisingly, this works out pretty well for him. Not so much for Cushing, though, as the twist ending (which, alas, is entirely too predictable) bears out.
One decade later, Peter Cushing and Christopher Lee appeared alongside fellow horror legends Vincent Price and John Carradine in 1983's House of the Long Shadows for Golan and Globus's Cannon Films. Directed by Pete Walker, the film's ostensible star is Desi Arnaz, Jr., who plays a cynical author who bets his British publisher $20,000 that he can write a potboiler in 24 hours, but he's upstaged by the old pros at every turn. Choosing a long-abandoned manor house in Wales as his base of operations, Arnaz taps out the first sentence of his novel and then immediately goes exploring, whereupon he encounters creepy caretaker Carradine and his daughter (Sheila Keith in a role originally earmarked for Elsa Lanchester). He's also surprised by a young woman (Julie Peasgood) who insists he's in great danger and tries to get him to leave, but he's having none of it.
In short order, they're joined by Cushing (who claims to be a stranded motorist and comes equipped with a speech impediment that he must have borrowed from Michael Palin), Price (who calls the manor his ancestral home and warns, "Please don't interrupt me when I'm soliloquizing"), and Lee (who's buying the property and is more than a little surprised to find it occupied by such riffraff). Nothing is as it seems, though, and soon the conversation turns to a brother Roderick who, yes, has to be "weleased" and starts thinning out the cast, roughly in the order in which they were introduced -- with the notable and unfortunate exception of Arnaz. Also unfortunate is how long stretches of the film play out in almost total darkness, such that it's impossible to tell who's doing what to whom at any given moment. A suitable alternate title might have been House of the Insufficient Lighting.