Yes, that IS Tigershark and Angelina as they appeared in the first novel of the Gemutations series, Mercenaries and Angels.
The Second Edition recently was released in April 2015, a revision of grand magnitude which doubled the length of the book and cleaned up the inconsistencies from the previous iteration.
David wasn't always as nice as he is in Plague... in fact he WAS the bad guy in Mercenaries and Angels, and nearly Angelina's death more than once!
I encourage my readers to give the novel a try! If you like Plague, you'll love their origin story! :D