"Mark Phillips" is, or are, two writers: Randall Garrett and Laurence M. Janifer. Their joint pen-name, derived from their middle names (Philip and Mark), was coined soon after their original meeting, at a science-fiction convention. Both men were drunk at the time, which explains a good deal, and only one has ever sobered up. A matter for constant contention between the collaborators is which one.
Originally published as That Sweet Little Old Lady, Brain Twister follows the adventures of FBI agent Kenneth J. Malone as he attempts to unravel the machinations of a telepathic spy. His first problem: how do you find a telepath to catch the first telepath?
The novella was nominated for the Hugo Award in 1960. (Summary from the text and Catharine Eastman)