When Darkness Falls

After Dumbledore is killed while dueling Voldemort in the Atrium at the Ministry of Magic, the existence of Harry's secret older half-sister, Lorelei, comes to light. How will Harry adjust to having a very Slytherin older sister? How will Severus handle his strong attraction to her? And how will everyone handle her very big secret? – A/U, OOC [SS/OFC, HP/DM, HG/RW, BZ/GW]