What is a short summary of the story, Calm Your Horses, from the collection, Young Skins?

“Calm with Horses” follows Douglas “Arm” Armstrong, a man in his mid-twenties. He is unmarried, but he has a five-year-old son named Jack. Arm is on good terms with the mother, Ursula, but Arm is only occasionally involved in helping to raise Jack. Arm works as an ‘enforcer’ for the small, illegal cannabis business that operates in town. The operation is organized by Arm’s friend Dympna. Dympna’s uncles, Paudi and Hector, grow and supply the cannabis. One night, one of the dealers who works for Dympna attempts to sexually assault one of Dympna’s sisters. Dympna’s uncle Hector says that they should kill the dealer. Arm, fearing the uncles will halt the business if he does not comply, kills the dealer. When Arm and Dympna go to talk to Paudi, Paudi mistakenly thinks they are threatening him. Paudi attacks them with a gun. Dympna appears to die, and Arm eventually escapes. He sustains an injury but does not go to a hospital. He dies of blood loss a few hours later.