His back was towards them.

Presently he turned, carelessly looked up at the window, and then, as if undecided what to do, took off his cap and scratched his head.
"It is Mike, sure enough," Desmond exclaimed, and, thrusting his hand through the bars, waved it for a moment.
Then, taking the little packet, he dropped it.

Mike put on his hat again, turned round, then looked cautiously to see that no one was noticing him, and strolled, in an aimless and leisurely way, towards the wall.

Desmond could no longer see him, but felt sure that he would find the missive.
Presently he came in sight again, walking quietly away.

He did not look round; but when nearly at the bottom of the hill turned, lifted one hand, and disappeared behind some houses.
"He can't read," Desmond said, "but I have no doubt he will get someone to do it for him." A vigilant watch was kept up, but nothing was seen of Mike, till late in the afternoon, when he emerged into one of the open spaces.