To make matters worse, Laura told me that her Sylvester always runs away and hides from strangers, so I was not expecting a warm reception from him in the tree. I needed to approach him as calmly and gently as possible, so that's what I did.
I prepared the cat bag on my arm and then made the mistake of reaching that same hand out to him again. This time, he sniffed and reacted with flattened ears and a hiss. He didn't explain the reason for this sudden change of heart, but I suspect he was not happy about the scent of other cats from my cat bag. Now, I was worried about running out of time before he decided to climb higher to get away from me.
Laura took him inside and released him, and Sylvester was happy to settle back into a comfortable home. Laura sent this picture of him sleeping to me later that day.