Wash and stone the plums. Put red wine, vinegar, sugar and cinnamon stick into a pot and bring to the boil while stirring. Add the plums and bring to the boil briefly. Remove from the heat, add rum and stir.
Pour the plums into 2 prepared jars and close them well. Leave to stand for at least 1 day. Tastes good as a side dish with game and other dark meat, but also as a dessert.