When Roderick Usher sends a letter begging his old school friend to visit him, it becomes apparent that he is suffering from a severe mental illness caused by an extreme overload of his senses. His sister too is very ill, suffering from cataleptic deathlike trances.
When Roderick announces that his sister has died, and they place her coffin in the vaults of the House of Usher for two weeks prior to burial, neither of them can imagine the horror which is to follow.
Poe at his most macabre.