who died?

at the beginning of book four...
who died there? did voldemort faked his death, did his father die?
it couldn't have been voldemort, because his mother was there, who died at his birth, but if it was his father, did voldemort killed his grandparents as well? how old was vldemorts father? would he go out with his parents if he has a 16 year old son and where was his son, when he wasn't at hogwarts.....???

voldemort killed his dad and grandparents. after voldemorts mother died, his father went back to live with his parents at the Riddle House

ah, thx =)