You arrive at Tianshi Mo's old residence and find a letter left behind by his friend.

There's a letter...

The date written on it is several days ago. Your mentor did indeed come back here.

"We shall meet at Serenity Garden and discuss the promise at length"... Mr. Mo is going to meet someone at the Garden tomorrow...

The letter is anonymous. But the tone tells me it's from someone close to Tianshi Mo.

We finally got a strong lead! Let's look around some more.