According to their website, Waterstones Clapham Junction is in Battersea! The area is not part of London that we were familiar with, but is a nice area, especially the nearby Northcote Road, which has been (possibly temporarily?) pedestrianised and is full of independent shops and places to eat. After that we walked across Wandsworth Common towards our next stop of the day.
Northcote Road (left) and Wandsworth Common (right)