Place the first 4 ingredients together in a saucepan over a medium heat and stir frequently until the sugar is fully melted. Keep a close eye on the pan - the sugar can (and will!) burn very easily.
When the sugar is melted, pour in the red wine, grapefruit juice and orange juice. The sugar will probably solidify at the bottom of the pan. Just carry on stirring and it will melt again eventually.
When the sugar has melted, leave the wine to gently simmer for around 15 minutes to give the flavours time to infuse.
Remove the saucepan from the heat and stir in the vodka.
Sieve the wine into a jug and serve.