All that day I lay in the dungeon cudgelling my brains for the reason of this new and inexplicable punishment.

All I could conclude was that some stool had lied an infraction of the rules on me in order to curry favour with the guards.
Meanwhile Captain Jamie fretted his head off and prepared for the night, while Winwood passed the word along to the forty lifers to be ready for the break.

And two hours after midnight every guard in the prison was under orders.

This included the day-shift which should have been asleep.
When two o'clock came, they rushed the cells occupied by the forty.

The rush was simultaneous.