Have you read any Sally Beauman? I enjoy her books - they are well-written and intelligent, with very good plotting - a bit dark (but no more so than PD James!). I'm re-reading The Language of Love at the moment, and am really hooked on it, in spite of remembering the eendings. Minette Waters is also goodNeither Beauman nor Waters writes Whodunnits, but their stories usually have a mystery at their heart.

Enjoy your time off!