History and specifics
Born in New Orleans on Earth, Adams had a criminal record for using his biochemistry knowledge to scam potential customers. Around 2250, Dr. Adams was on board the transport ship Brass Ring when it was attacked by the Romulans; the result of his injuries left him with artificial intestines.
Around 2270, Dr. Adams — along with fellow researchers Sepek, Yoshi Takhumara and Lara Krovazhadny — was assigned to a secret research base on the planet Tanis, operated by a clandestine group of Starfleet admirals led by Rodrigo Mendez, the head of weapons research. Their connection was also somewhat personal; Mendez had lost his wife on the Brass Ring, and Yoshi — another survivor of the incident — was his son. They were assigned to work on a virus intended for use against the Romulans, dubbed the "R-virus". The Vulcan researcher Sepek — who had deceived Mendez into believing he was a rogue — was killed using this virus; however, it accidentally mutated into a form contractible by humans, the "H-virus". Adams, Yoshi and Lara were infected, and Adams sent out a distress call. However — driven by a maddening hunger for blood — he killed both of the others before he was discovered in the darkened base by a landing party from the USS Enterprise, responding to the distress call.
The virus had made Adams severely anemic and looking almost corpse-like; he was also incredibly photosensitive, so much that light burned holes in his skin. Held in a dark isolation chamber onboard the Enterprise, Dr. Adams responded truthfully to computer-monitored questions regarding his work on Tanis (claiming it was "agricultural research"), and denied having killed either Yoshi or Lara, but Dr. Leonard McCoy — observing his demeanor through infrared camera, seeing Adams smile in the darkness — was not convinced; he speculated that Adams was sociopathic. Despite apparently being "innocent", Adams lured Nurse Christine Chapel into his isolation chamber by faking choking on his food, knocking her unconscious (infecting her via contact with a wound in her head caused by the fall), and attempting to escape isolation, only to be trapped in the brightly-lit airlock.
Restrained in isolation afterwards, Adams confessed to Captain James T. Kirk that he worked for Admiral Mendez, and that Mendez would kill him if he was left in his custody to prevent word of a secret weapons project run by Starfleet officers. Though he was reluctant to believe it, the idea unnerved Kirk enough to question Mendez's motives; nonetheless, the Enterprise turned Adams over to Mendez at Starbase 9 and thought that would be the end of it. However, Adams escaped his imprisonment, killed a trader captain and stole several items from her body, including a hooded robe and a communicator that could send a message into the Romulan Star Empire. Taking Ensign Lisa Nguyen, a member of the security crew, at phaserpoint, Adams returned to the Enterprise. Seeking to stabilize his condition long enough for a rescue, he broke into the quarters of Ensign Jonathon Stanger — whose blood type matched his own — and gave himself a transfusion while Stanger slept, then hid in the bowels of the Enterprise.
In time, however, Adams was captured by the infected Stanger just as a cure for the H-virus was discovered, and a Romulan bird-of-prey arrived to "rescue" him - and retrieve the R-virus sample, which Adams carried in a pendant around his neck. Admiral Mendez, Dr. McCoy and Commander Spock had been on Tanis' surface searching for the same sample, and were captured by the Romulans. After the Starfleet officers had escaped back to the Enterprise and Mendez had started issuing threats unless he was given the virus sample, Kirk brought Adams (in a containment suit) down to the transporter room. Adams played on Mendez's fears of infection by lowering the force field around his containment suit and touching the admiral on the arm. As a sobbing Mendez collapsed to the floor, Adams commented that it was unfortunate he had already been cured, for he had "wanted to do that for a long time". Adams and Mendez were then taken into custody. (TOS novel: Bloodthirst)