You control Toby, whose goal is to find Bishop's nephew. To move a dog, click. When footprints appear, it means that you're going in a good way.
Climb on stairs and click on an icon of dog's nose: Toby will catch a scent.
Turn left and go under a wooden landing at a building and go with it.
Go down the boxes-crate, opposite to the pub entrance
and enter another ramp.
Turn right and notice Henry's scent (icon of dog's nose).
Go under door of another building, leave a ramp and run forward.
Enter the building with the left door. Turn left and enter next room via the passage on the right. Move to the another room.
Pay an attention to a lever, but, unfortunately, it is stuck.
Return to exit door and go forward to leave the building from the other side.
Click an icon of dog's nose again.
Run forward to barrels in the corner and point at the one with grease on the top.
Return under the door at which pales are sticking out of the water. It seems that Henry moves on the other side, so Holmes and Toby have to go there too.
Enter the building with a lever again and go to the room with it.
Once again, point at a lever - oil it with grease. Exit the building at the side of pales sticking out of water.
You have to cross on the other side, jumping on other pales. Enter a ramp on the left
and jump on the next pales (route as on the picture above) and on the wooden platform.
On the other side, jump on a machine which lowers the bridge. Thanks to that Holmes will join Toby.