Books about brainwashing/sleeper agents

I recently picked up Faded Memory by Dean Koontz and loved it. It was great reading as the character gradually realized that some of them had indeed been brainwashed by accidentally activating each other. It was also great to go back to some previous chapters and see the abrupt shift in thought patterns as the conditioning triggered or the hints to characters missing time.

I'm looking for more books featuring stuff like sleeper agents – not super picky on genre so long as it's Fiction and ideally NOT High Fantasy. Grand conspiracy is optional.