The Challenge — Susan Kearney

SHE WAS SHOT PROTECTING THE PRESIDENT, AND WOKE UP NAKED, IN THE ARMS OF A HUNK...
... a hunk named Kahn, who told Secret Service agent Tessa Camen an outlandish story about traveling through time, saving the world, and a Challenge only she can accept. Kahn offers her proof she can't refute and Tessa must accept that she has been brought forward through time to save Earth by winning an intergalactic challenge.

Kahn only has a few weeks to train Tessa to use the psi-abilities he insists she has. He is confident in the success of a time-honored method that uses sexual frustration to bring out her powers, but Tessa is dubious. She's a martial arts expert and can fight her way through any-thing, but she's never had much luck with emotions.

Luckily for Earth, Kahn can be very convincing...