Star Trek Section 31 Series 1-4 by Various Authors

Star Trek : Section 31 - 1 - Cloak - S. D. Perry
Once, in order to preserve the galaxy's fragile balance of power, Captain James T. Kirk carried out a dangerous mission to capture a cloaking device from the Romulan Star Empire. Months later, while investigating a mysterious disaster aboard a Federation starship, Kirk discovers that the same technology he obtained for the sake of peace is being put to sinister purposes. What the crew of the Enterprise uncovers will send shock waves through the quadrant, as Section 31 sets in motion a plan that could bring the major powers of the galaxy to their knees.

Star Trek : Section 31 - 2 - Rogue - Andy Mangels & Michael A. Martin & Gene Roddenberry
Six months before their battle against the Borg for the fate of Earth, Captain Jean-Luc Picard and the crew of the USS Enterprise-E face a very different kind of crisis. A world in turmoil becomes the focal point of conspiracies and betrayal as an unexpected reunion brings with it startling revelations. Old friends become bitter enemies and one young officer reaches a crossroad when he's forced to choose between the greater good of the Federation and the ideals for which it stands.

Star Trek : Section 31 - 3 - Shadow - Kristine Kathryn Rusch & Dean Wesley Smith
Someone or something is trying to kill Seven of Nine. As the crew races against time to save millions of refugees from an imminent stellar cataclysm, the former Borg becomes the target of several seemingly random but potentially lethal "accidents." The investigation reveals a truth more terrifying than anyone ever imagined, as Captain Kathryn Janeway and the crew of the Starship USS Voyager fight for their lives against the most unexpected enemy of all.

Star Trek : Section 31 - 4 - Abyss - Dean Weddle & Jeffrey Lang
Mere days after the startling events of Avatar, Doctor Julian Bashir faces his darkest nightmare when Section 31 compels him to undertake a mission to stop one of their own. But this renegade is no ordinary agent. Like Bashir, Dr. Ethan Locken is genetically enhanced, a Human superior in body and mind. But Locken dreams of remaking the galaxy in his own image – and creating a new human empire based on the example of the infamous Khan Noonien Singh. And as he begins to understand the terrifying truth about his opposite number, Bashir will learn more about himself than he ever wanted.