Back at the Villeforts', Valentine is still green in the gills. She has been that way for four days now.
The Count of Monte Cristo appears in her room on the night of the fourth day, and he tells Valentine that he's been watching her from a room in the house next door. Every night he sees someone trying to poison Valentine, and every time that happens, the Count sneaks in and replaces the poisoned drink with a healthy one.
The Count tells Valentine to pretend to sleep the next time someone comes in and tries to poison her bedside drink. He tells her to try to discover who the poisoner is.