In the authorised continuation Miss Marple short story The Unravelling, Martin is a farm hand who works for Syme the farmer. In a strange incident, Martin helps Syme take his pigs to the village butcher. While waiting in the market square, Mr Weaver the haberdasher, comes out of his shop and tells Martin to move the pigs away. For some reason, Mr Weaver loses his temper and raises his fists. Martin steps back and trips and falls to the ground. Syme and the police Sergeant Dover intervene and break up the altercation but the next day, Martin is found dead, shot by an arrow.
The incident would appear so trivial that it would not seem motive enough for anyone to consider murder. Moreover, very little was known of Martin's background. He arrived and offered to work for Syme for food and a dry barn to sleep in. Syme was normally suspicious of strangers and agreed only because he was short-handed and because his dog seemed to have an uncharacteristic fondness for Martin.
It would be up tio Miss Marple to discern who Martin was and why he was killed.