The key was explained by a cage on a stool, and a bird flying out.

She had unlocked the cage for Patrick.
'He never seemed anxious to be released while he was at work,' said Jane, after she and the captain had spelt the symbolling in turns.
'And never thirsted to fly till he flew, I warrant him,' said Con.
A repeated sketch of some beauty confused them both; neither of them could guess the proud owner of those lineaments.

Con proclaimed it to be merely one of the lad's recollections, perhaps a French face.

He thought he might have seen a face rather resembling it, but could not call to mind whose face it was.
'I dare say it's just a youngster's dream on a stool at a desk, as poets write sonnets in their youth to nobody, till they're pierced by somebody, and then there's a difference in their handwriting,' he said, vexed with Patrick for squandering his opportunity to leave a compliment to the heiress behind him.
Jane flipped the leaves back to the lady with stormy hair.
'But you'll have the whole book, and hand it to him when he returns; it 'll come best from you,' said Con.

'The man on horseback, out of uniform, 's brother Philip, of course.