Grosta was a Gorlan and the so-called "muscle" of Amanda Steele's pest control team.  

He and his team were hired by Georgia Donnelly, the owner of Funworld after the skeleton crew of Funworld had suddenly ceased communication following a message talking about a "predator."  

This predator turned out to be the Vashta Nerada who had wiped out the entire skeleton crew. He, his team and Georgia met the Fourth Doctor on Funworld. They discovered the truth of what had happened after Phelan created a psychic link between her and the Vashta Nerada. After Phelan was killed, he attempted to kill the Vashta Nerada by drawing them out with meat. However, they ambushed him and Amanda and destroyed him. (AUDIO: Night of the Vashta Nerada)

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