Double Helix 05 Double or Nothing by Peter Allen David

The sources present excerpts from a science fiction narrative, primarily focusing on two major interwoven plots: the capture and escape of Vandelia, an Orion woman, from the Thallonian Zolon Darg and her subsequent rescue by the Xenexian Mac (Captain Calhoun), and a Starfleet-centric mission to uncover a massive conspiracy led by General Gerrid Thul. The Vandelia storyline establishes her history as an Orion dancer living under a false Thallonian identity, Vara Syndra, to evade Darg, while the Starfleet plot follows Commander William Riker temporarily in command of the Excalibur after the Independence is destroyed by Romulans, ultimately revealing that Thul and the Romulans are working together from within a massive, cloaked Dyson Sphere. Thul's plan involves using stolen Starfleet technology, including the Omega 9 AI, to unleash a biological weapon called the Double Helix virus via the Federation's replicator network, but the heroes manage to infiltrate the sphere, defeat Thul and Darg, and prevent the widespread catastrophe.