She could not escape by the door of the room because he had the key in his pocket.

Li Choo was not a stern jailer, however.

Mazarine had not been gone three minutes before the Chinaman had touch with Louise.

He did more; he threw up into the open window of her room a screw-driver, with which she took the old-fashioned door off its hinges, after half an hour's work.

Then, leaving a note on the table of the dining-room, to say that she could not bear it any longer, that she would never come back, and that she meant to be free, she summoned Patsy Kernaghan and fled to the Young Doctor.
When Mazarine returned and found her note, he plunged up the stairs to her bedroom, his pious wrath gurgling in his throat, only to find the door locked; for Li Choo had promptly restored it to its hinges after Louise had gone, afterwards dropping from the high window like a cat, without hurt.
Li Choo, blinking, opaque, immobile, save for his piercing and mysterious eyes, had no explanation to give.