Roscoe is not mentioned in the main series prior to Plague, however he plays a large role in Sinder's story. (www.thefayz.com)
The first we know of Roscoe is that he is a boy working for Albert, responsible of collecting the food that Hunter brings for the Perdido Beach kids. He is likely to be attracted to a fellow female collector. After Hunter has killed his competitor Old Lion, and is delivering it's meat to Perdido Beach, Roscoe is bitten by one of the Bugs that Hunter had unfortunately acquired. Most people thought nothing of it until Taylor spread the news of Hunter's horrible death and a worried Edilio had to take action.
Edilio placed Roscoe in a room in the town hall, telling him it was for his own protection, and Roscoe accepted this calmly. But later, as the bugs started emerging, Roscoe lost it and started screaming for help and to be let out, but the only response was from a terribly saddened Edilio who locked the door and boarded up the windows. Roscoe was the only living victim of the bugs and Edilio was set out to make sure nobody else got it. However, this didn't work and lots of people got it, even Dekka (a lead character.)
Later, Roscoe was noted dead inside the room as the bugs had eaten him and then escaped the room easily despite Edilio's efforts.