Logan is a law-enforcement official for the Gene Protection Agency (GPA), tasked with tracking down illicit genetic-engineering operations. Carrying the heavy legacy of his mother's role in the Great Starvation, he operates with a deep sense of guilt and obligation. He is a dedicated family man whose life is upended when a routine raid exposes him to a genetic-altering agent, causing unprecedented changes to his physical and cognitive abilities.

Kara is Logan's sister and a former special-forces operative with a worldview shaped by past trauma. Unlike Logan, who feels a sense of duty to fix their mother's mistakes, Kara is highly pragmatic and deeply affected by her military experiences. Her capabilities and perspectives shift dramatically as she undergoes her own genetic upgrade, setting her on a collision course with her brother.

Edwin is Logan's superior at the Gene Protection Agency. As a government agent, he manages complex ethical boundaries in his pursuit of public safety, often prioritizing the agency's mission over the individual rights of his employees. He acts as the primary point of contact between Logan and the GPA leadership regarding the nature of Logan's mysterious illness and genetic alterations.

Miriam is Logan and Kara's deceased mother and a brilliant geneticist. Her attempt to genetically fortify crops caused a global famine that killed 200 million people, leaving a dark legacy that defines her children's lives. Prioritizing scientific breakthroughs over her family, she leaves behind a complex technological and ethical footprint.

Beth is Logan's wife, providing a stable and intimate domestic life that contrasts with his traumatic past. She understands the heavy guilt Logan carries regarding his mother's legacy, though she worries about his decision to work for the GPA. She offers an emotional anchor for Logan as he experiences sudden changes to his mind and body.

Ava is Logan and Beth's teenage daughter. She shares a close bond with her father, often engaging him in competitive games of chess. She struggles to process her connection to her infamous grandmother, keeping her lineage a secret from her boyfriend and peers.

Nadine is Logan's partner at the Gene Protection Agency. Having worked together for three years, she shares a close professional intimacy with Logan, understanding his nerves and habits before a raid. She serves as a dependable ally in the field as they enforce the government's strict ban on genetic modification.

Max is Logan's twin brother who died when they were young. His early death severely impacted the Ramsay family, contributing to the emotional distance and ongoing trauma experienced by Miriam, Logan, and Kara.

Dr. Strand is Logan's longtime internist. He is the first medical professional to notice the strange anomalies in Logan's bone density and order the DNA analysis that reveals his genetic alterations.

Dr. Romero is a respected geneticist who is forced to halt his scientific inquiries due to GPA regulations. He holds a firm belief that scientific knowledge cannot simply be hidden away once discovered, a sentiment he shares directly with Logan.

Henrik Soren is a suspect taken into custody for associating with illicit-market genetic-engineering operations. The address he provides under interrogation leads Logan directly into the explosive trap that alters his DNA.

Feld is an illicit genetic modifier who maintains an off-the-record arrangement with the GPA. This status as an informant allows him to continue his controversial work while under loose government surveillance.

Alexei is one of the guards protecting Feld's laboratory and menagerie of engineered organisms. He follows orders to escort visitors through the heavily fortified building.

Tiffany is a resident of Glasgow who experiences sudden genetic modifications during a mysterious, fatal outbreak that forces the quarantine of her entire town.