Why did Watson agree to visit Stapleton ? Chapter7

Stapleton wanted Watson to meet his sister. Watson agrees because Sir Henry was busy when he left and had also noted that he wanted him to meet the neighbors.

"A moderate walk along this moor-path brings us to Merripit House," said he. "Perhaps you will spare an hour that I may have the pleasure of introducing you to my sister." My first thought was that I should be by Sir Henry's side. But then I remembered the pile of papers and bills with which his study table was littered. It was certain that I could not help with those. And Holmes had expressly said that I should study the neighbours upon the moor. I accepted Stapleton's invitation, and we turned together down the path.