Who bursts into Thrushcross Grange while Nelly is tending to the baby in Chapter 17? Why?

Isabella tells Nelly that Hindley did not attend Catherine's funeral, because he could not keep himself sober. Heathcliff had been absent for nearly a week, roaming the moors and coming home at dawn. He would lock himself up and recite terrible prayers, then head down to the Grange.