Vin was an ex-soldier who was recruited by the Eleventh Doctor to help him protect a Terraform. Meeting the newly arrived Doctor in a station, he accompanied the Doctor and his beautiful companion to a makeshift camp to grab the Terraform.
In order to help Amy and Banardo, he fired a spraying shot into the centre of the camp, momentarily giving a distraction. After capturing it he helped to escape with it on a runaway train. When he was brutally shot by one of Captain Britt's men, the Doctor removed the bullet from his shoulder.
He didn't believe the Doctor's stories about aliens, but quickly fell for it when seeing a flying saucer in the sky and then seeing the creature that emerged from its ruin in the ground. His reward for his help was an allotment given by the Doctor. (AUDIO: The Runaway Train)