PLOT As  Lord Voldemort  retrieves the  Elder Wand  from  Albus Dumbledore 's tomb,  Severus Snape has become  Hogwarts ' headmaster. Meanwhile, after burying  Dobby ,  Harry Potter  speaks with the goblin  Griphook  about breaking into  Bellatrix Lestrange 's vault at  Gringotts  bank, suspecting that a  Horcrux  may be hidden there. Griphook agrees