Dumbledore's Army and the Year of Darkness (DAYD) is an alternate 7th year story following the formation and actions of Dumbledore's Army under the command of the main character, Neville Longbottom. it takes place during the final battle of Hogwarts i.e. the Second Wizarding War.
Hogwarts is under the control of the Carrows and Snape and Dumbledore's Army is now the resistance. Students become soldiers as they prepare for a war.