Turn Up For The Book Meaning

(idiomatic) a very unexpected, usually pleasant, surprise.

Example:   When it was finally time to board, we got on the train to find out that we’d been put in business class. This was a turn up for the book, reclining seats and room to stretch out a little.
1987: Edward Dryhurst, Gilt Off the Gingerbread
  Her mother kept well away from us, which was a turn up for the book, and for the time being at any rate, I was a model husband.