Harsh and unforgiving, Thread appears in Catching Fire, ready to enforce the law, no matter what. Being fiercely loyal to the Capitol, he is willing to do whatever it takes; going to such an extremity that he injured Katniss, the victor of District 12 who had an upcoming modeling session.
At one point, Thread brutally beat Gale Hawthorne, who had been caught poaching a wild turkey. Although Gale had been selling meat to the Peacekeepers of District 12 for years, they never turned him in for their own stomachs. In Thread's case, he sees this as extremely punishable, threatening to kill Katniss or Gale if he saw either one of them in the woods. Darius had tried to save Gale from his punishment, but ended up severely injured.
After that display of vast cruelty, people stayed inside their houses, rather then risking the wrath of the new band of Peacekeepers. Katniss goes to her house as well. A few days later, Katniss sneaks out of her house and goes to the woods where she meets Bonnie and Twill. After returning, Peacekeepers were sent by Thread to deliver a message to Katniss; the fences will now be electrified 24/7.
It is later revealed that Darius had probably been turned in to the Capitol by the Peacekeepers lead by Thread. Due to this, Darius was made an Avox specifically as a warning to Katniss.
It is unknown if the capitol got him out before the bombing, but if they did not, he was excecuted by the Rebels.
Thread works as the new Head Peacekeeper in District 12, replacing Cray, the previous Head Peacekeeper. Being the new Head Peacekeeper, he has to enforce the peace. If any laws are broken by anyone, he will have to deal with the punishment. As the Head Peacekeeper, he has to go by the District Protocol when carrying out punishments. This fact is proven when Purnia had to tell him about District 12's protocol (for instance, the amount of whippings one is supposed to receive, and what is punishable by death).
As part of his leadership, he can command the other Peacekeepers to carry out procedures (such as when he ordered the Peacekeepers to send a letter to Katniss, or when he made sure of the fence's security).
Thread is terribly loyal to the Capitol, and doesn't mind sacrificing morals or standards to get the job done.
Thread, as Katniss explains, has close cropped hair and dark gray eyes, not like in the Seam. He looks especially mean with his new Peacekeeper uniform.