Those who move slower and take their time can usually avoid error. Those who move quickly mess things up and can literally “fall.”
In paragraph 9, what the phrase "drew him on by artful questions" means is that he questioned him to try to gain privileged information.
He had to find out some information that was very important to him, so he started questioning him furtively so as to get to the bottom of things.
The stranger's interaction with Elisa was a bit awkward since they were not introduced formally and Elisa was a bit professional as she entertains the stranger. On the other hand, Elisa was comfortable with Henry since they have been friends for a while already.
