Case 4 - Chain Reaction.
After recreating the events leading to the accident, Holmes will venture into London's Sewer system.
This achievement is really difficult I confess I needed to turn to a guide.
To unlock the achievement Holmes must successfully use the water pressure mechanisms to help him reach a section of the sewers.
These the correct steps to follow:
1. At first water mechanism set water level to 0;
2. Descend the ladder;
3. Push the platform as far forward as possible;
4. Return to mechanism & set water level to 1/2;
5. Use the risen platform to Jump to the other side;
6. Walk to the other side by using the metal pipe;
7. At next water mechanism Set to 0;
8. On wall to the right is a wheel, use to move the ladder to the left;
9. Walk down and push the platform towards the ladder;
10. Go back and set the water at 1/2;
11. Use the lever on the left side and lower the bridge;
12. Walk back across bridge, go down the small ladder and jump onto the platform
13 Jump across platform to the other side;
14 Go up, use the mechanism and walk through the door.