When you get to the place, go forward and after a while you'll be talking with a Henry's Hampford, a Bishop's nephew, housemaid. You'll get a permission for searching his garden.
The gate to a garden is at a wall, on the left side of house. Open it and go forward.
Look at a hanging laundry. Watson will notice, that one piece is missing. Pick up remaining clothes pegs.
Open a shed, which is on opposite to the hanging laundry, and take a pickaxe. Holmes will notice that a shovel is missing.
Steal also rake from vegetable garden.
Go deeper in a garden, to the right corner, and notice wired tins, which is an intruder alert. Click on it.
On the other side of patch (next to laundry and exit) and spot a hole in a fence.
Use a rack on nails in the fence. Holmes will make a passage to the next part of garden. Go there.
Look through the hole in a fence, you'll see a nephew's window.
On the barrel you find "The Strand" pick it up. It from before four days, what means that Henry was being observed from this place.
On the other barrel notice remainings of a small meal.
Go further. Find a stolen laundry on a corner tree. Use rake to get tattered clothes (what gives you another achievement: "Garden Gumshoe").
Leave a garden and knock at the front door to inform a housemaid that you've found a laundry. Thanks to that, she'll let you enter Henry's room.