This is book 6 of the "Spenser" series.

This note contains spoilers for the book.

Probably the best Parker novel. Spenser is picked to bodyguard a radical lesbian feminist writer. And then fired. And then she is kidnapped, and he has to find her anyway, even though she disapproves of many of the things he practices.

There's a lovely scene where Rachel asks Susan if Spenser protects her, and she responds that they protect each other -- she's doing it now.