Apparently, Nan got into some cherry brandy that Mrs. Jewkes had left lying around accidentally on purpose.
Mrs. Jewkes told her to sleep it off upstairs, so when Pamela and Mrs. Jewkes went up to bed and found "Nan" asleep in the chair with her apron over her head, Pamela thought nothing of it.
Duh dun dun.
Pamela undresses while telling Mrs. Jewkes the entire history of her misfortunes in Mr. B's employ and her take on these events.
When they get in bed, Pamela lets her right arm to be pinned beneath Mrs. Jewkes so she could keep her hands close to the keys around Mrs. Jewkes's wrist.
When Pamela heard "Nan" stir, she tried to get her to come to bed. She got no verbal response, but eventually "Nan" started undressing, hidden by a nearby curtain.
To explain "Nan's" unresponsiveness, Mrs. Jewkes reminded Pamela that she had told Nan not to talk to her.
"Nan" then gets into bed and … it's Mr. B. Eeeeeek!
With Mrs. Jewkes and now Mr. B restraining her arms, Pamela was unable to move.
Before escalating the assault, the master tried to convince Pamela to accept the proposal he had made to her in writing, saying he would leave her alone now if she did.
Pamela (of course) faints and has some kind of intense fit for so long that Mrs. Jewkes and the master think she's dying.
She woke up to Mr. B soothing her, and she was terrified that he had continued his attack after she passed out. He promised he didn't, but now that she's feeling better …
Pamela faints again.
When she wakes up the second time, she's alone with Mr. B and Nan. He's super apologetic and even seems sincere.
Tuesday morning, the master calls Pamela to come down to him. He promises not to attack her again, says he loves her, and claims he can't live without her.
So, she still can't leave. But he does ask her to (1) promise that she will stick around for another two weeks and not try to go anywhere without his consent and (2) forgive Mrs. Jewkes for aiding and abetting.
Pamela agrees, and signs off noting that the master now talks freely of loving her and tries to kiss her frequently, which Pamela doesn't like (even though the master tries to pass it off as "innocent") (64.49).