Secret Asset - Stella Rimmington

Why is it that 390 pages can seem like a hard slog with some books and a walk in the park with others? Secret Asset is a really quick read not that there isn't a good story. Liz Carlyle from "At Risk" returns and this time she's tracking down a mole within MI5. There are enough clues to guess the mole's identity before the end of the book but that isn't the point. Once you know who this person is you can see the damage they can do. Ending weakened the book a little but hopefully Liz will be back.