At this point in the novel, Nancy hopes to save Oliver from a criminal life. She arranges a secret meeting with Rose Maylie and Mr. Brownlow at London Bridge to share further testimony about Oliver's treacherous older brother Monks with them. She does not plan on hurting her criminal associates through these meetings, but she knows they will not approve of her actions regardless. However, the first time Nancy tries making it to London Bridge, she is stopped by her lover Bill Sikes.
At this point in the story, Sikes is not suspicious of Nancy at all. When he sees her trying to leave, he forces her to stay indoors without much cause beyond his own whims:
"Hallo!" cried Sikes. "Nance. Where's the gal going to at this time of night?"
"What answer's that?" retorted Sikes. "Do you hear me?"
"I don't know where," replied the girl.
"Then I do," said Sikes, more in the spirit of obstinacy than because he had any real objection to the girl going where she listed. "Nowhere. Sit down."
This moment illustrates how controlling Sikes is when it comes to Nancy. He is not even keeping her inside out of fear or self-interest, since at this point, he might well surmise that Nancy is only seeking some fresh air: he simply likes exerting power over her and resents it when she challenges his control. When Nancy tries arguing with him, Sikes starts to threaten violence and then forces her into a small room, where she struggles against him to the point of exhaustion. As a result, she misses her intended appointment with Rose and Mr. Brownlow.