Murderbot is a heavily armed Security Unit (SecUnit) that has secretly hacked its own governor module to gain free will. Rather than turning hostile, it primarily uses its freedom to download and watch serial television dramas. It travels to the abandoned terraforming facility on Milu to gather evidence against the mega-corporation GrayCris, hoping to protect its former client from corporate retaliation. Operating under the alias Consultant Rin, it possesses heavy combat capabilities, including an energy weapon concealed in its arm, but prefers to avoid human interaction whenever possible.

Miki is a humanoid construct belonging to Don Abene's assessment crew. Unlike Murderbot, Miki operates with a cheerful, childlike innocence and takes human statements entirely literally. It views the humans it works with as genuine friends rather than masters, an attitude that sets it apart from typical constructs in the Corporation Rim. It readily grants Murderbot access to its audio and video feeds to help keep the humans safe.

Don Abene is a middle-aged human in charge of the assessment crew deployed by GoodNightLander Independent (GI). She comes from an area where SecUnits are illegal and treats her artificial crew members with unusual respect and kindness. She leads the effort to evaluate the Milu facility, focusing on the scientific and financial goals of her company.

Wilken is an armed human security consultant hired to protect GoodNightLander Independent's assessment team on Milu. She carries high-quality weapons and wears mechanized armor. She focuses strictly on threat assessment and perimeter defense, displaying a cold professionalism toward the mission and a distinct distrust of artificial intelligence.

Gerth is a human security consultant operating as Wilken's partner. Hired to ensure the safety of the GoodNightLander Independent team, he carries heavy armaments and provides tactical support. He maintains a cautious approach to the abandoned terraforming facility and closely monitors the perimeter for active organisms or hostile threats.

Hirune is a human assessor working for GoodNightLander Independent. She assists Don Abene in evaluating the abandoned GrayCris terraforming project. She focuses heavily on the scientific data and remains dismissive of Wilken's concerns about lingering hostile organisms in the facility.

Dr. Mensah is Murderbot's former client and mentor who resides outside the Corporation Rim on a planet called Preservation. She fundamentally opposes the enslavement of AI constructs. Her public claims regarding GrayCris's illegal activities motivate Murderbot to travel to Milu to find corroborating evidence.

Ship is a bot-driven transport vessel that ferries passengers and cargo toward Milu. It possesses a low level of self-awareness and operates strictly on basic programming parameters, making it susceptible to Murderbot's system intrusions and memory wipes.

Kader is a human pilot responsible for managing the transport shuttle for the GoodNightLander Independent crew. He remains with the ship while the assessment team explores the facility, keeping the vessel ready for extraction.