I Will Fear No Evil is a science fiction novel by American writer Robert A. Heinlein, originally serialised in Galaxy (July, August/September, October/November, December 1970) and published in hardcover in 1970.

The story takes place in the early 21st century against a background of an overpopulated Earth with a violent, dysfunctional society.

Elderly billionaire Johann Sebastian Bach Smith is being kept alive through medical support and decides to have his brain transplanted into a new body.

Smith omits to place any restriction on the sex of the donor, so when his beautiful young female secretary, Eunice Branca, is killed, her body is used—without his knowledge and to the distress of some of those around him.

Jake has a massive rupture of a large blood vessel in his brain and dies, but his personality is saved and joins Smith and Eunice in Joan's head.