That means you could get the whole series for under £4/$4! A pretty good Bank Holiday treat.
Each book can be read as a standalone, but if you want to read them in order it's even better.
First is Storm Rising:
Second is Rhythm of Deceit.
Next comes Cobwebs in the Dark:
And finally, The Girl in the Painting - set in romantic Paris, both in present day, and in the 1920s
Just click on any of the above pictures and a link will take you directly to Amazon. Happy Reading!