Plinn was a Retellian man that owned a freighter with his brother, Goff.
In 2152, they attacked a Kriosian transport and kidnapped First Monarch Kaitaama with the intent to hold her for ransom. After the kidnapping attempt, their ship's life support systems were in need of repairs. Enterprise NX-01 offered assistance with the repairs, and Trip Tucker transported to their ship. Plinn and his brother boarded the Enterprise and had a meal with Captain Archer.
During the repairs, Tucker discovered that the woman was a prisoner. Plinn was abandoned by his brother, who escaped to their ship, and Plinn was arrested by Archer. Archer tricked Plinn into providing information so they could track down his brother. They pretended he would face a tribunal with T'Pol as judge and that she always handed down harsh punishment. Afraid, Plinn revealed the information they need to find Tucker.
Tucker and Kaitaama were rescued after they had escaped from Goff and knocked him out. (ENT: "Precious Cargo")
Plinn was played by actor Leland Crooke.
According to the script, his second name, which he shared with his brother, was Firek.