This is a guide to getting into the watch customs office in A Grave Matter in Thief 2014.
Getting into Yellowface’s Office in Taking a Fence: http://wp.me/p1SfP0-1I6
All side mission guides: http://wp.me/P1SfP0-1Hf
All Thief guides: http://wp.me/P1SfP0-1FJ
Getting into the Watch Customs Office
Keep going up the street past the building which has the objective marker inside until you walk underneath a building. Shoot a rope arrow through a hole in the floor of the building and climb up:

Shoot a Rope Arrow at the Highlighted Beam to get into the Watch Customs Office in A Grave Matter in Thief 2014
Be sure to jump towards the left wall to avoid triggering a trap. Grandpa’s Ashes are in one of the cupboards.