Marphos is a water demon that possesses a local high school cheerleader named Deirdre Donovan. It is attracted to water and uses drowning as its method of killing, having already killed a man by drowning him at the bottom of a pool. The demon sacrifices victims as part of a larger plan, and when killed by Hub, its body bursts into flames even while in water.

Hub takes his son Cade along as a driver and lookout during the hunt for Marphos. Cade is unaware of the full truth about Hub's job as a demon hunter. Hub uses Cade as a distraction to escape from the sheriff after killing the demon, instructing him to drive away when the sheriff arrives.

Hub and Maryanne have a tense relationship, especially regarding their son Cade's upbringing. Maryanne wants to take Cade to Nashville, but Hub refuses, wanting to keep Cade away from the music business. Hub also tries to turn Cade against Lucky, Maryanne's boyfriend, by showing Cade Lucky's criminal record, which hurts Cade emotionally.

Sheriff Ruby arrives at the community pool to investigate after the demon's victim is found drowned. Hub tries to hide from her and uses Cade as a decoy to distract the sheriff so he can escape. The sheriff's investigation adds pressure to Hub's demon-hunting activities.

The demons in The Bondsman do not possess innocent victims. Marphos possesses Deirdre, a mean girl and local social media star who uses fake tears to manipulate others. The possession leads to real harm, including ritualistic murder by drowning, suggesting the demons target morally ambiguous or flawed individuals rather than purely innocent ones.