This issue is a variant of The Avengers (Marvel, 1963 series) #201 [Direct]. There exist further variants.
Adapted from Jim Shooter's short story "This Evil Undying" in "The Marvel Superheroes" 1979 paperback (Marvel Pocket Books #9) published by Pocket Books. Continues in the next issue.
Letters on The Avengers #196. Letters from Scott Peterson, John Merrill, Cindy A. Eager, Peter Petruski II, Johnny Hall