After skipping back to the Sigma series prequel and being really dissatisfied with it, I was pleased and relieved to find The Doomsday Key a return to Rollins's usual formula of mixing a little science with a lot of fascinating history, this time spanning the Celts, Irish saints, medieval plagues, primitive symbology, and more, all tied into modern genetically modified crops and the global food supply. Character development is handled just enough to distinguish this from the usual cardboard action figures and keep the tale engaging. Rollins veers close to preaching at a couple of points regarding the GM situation, but a) there are some rather terrifying things that everyone should know about GM crop research, regardless of one's political bent, and b) Rollins's pace throughout the book is so smooth and quick that there's little time to get bogged down in such discussions.

All in all, The Doomsday Key is impressively clever, entertaining, educational in all the fun ways, and a great addition to the Sigma line. If you like cliffhanger thrillers, you'll love this.