Irene Byers book The Sign of the Dolphin is the first edition [published date 1956].  This copy is in vg+ condition, a tight and bright copy in vg dust-jacket complete with unclipped price -- does have tears to spine area and chips to corners and crease at top. The boards are green with red titles to spine. Pages are bright and clean(for guidance on the grading of this book, please see below).  Hard to come by and has a dust-wrapper too.

Irene Byers, The Sign of the Dolphin, Hutchinson, 1956