First go to lara's house. Once there, lock butler into freezer then go to Lara's room. Open door and pick up flares. Go up into the attic. Use the flares and find the blue-green box and push it into wall. Then go to the library up stairs and push a book that is jutting out from the wall. This will turn off fire.

Go into the now extinguished fire place, and the left wall will be cimbable. Once up you will find yourself in a secret room. Vault up onto the ledge and push the top box over to the corner of the room. DO NOT GO OUT YET. First pull the lever showing you a secret door open. While you are being shown the door, press O.

Now you can go out. Sprint and jump over the banisters. If you've made it on time you should follow the hallways and end up in in the basement with an aquarium and another blue-green box.

Search outside of the aquarium for the key before going in it push L1 and up to look up and you will see a hole in the ceiling. Pull the box under the hole, and jump into it. follow this and it will go into the aquarium. Go to where you saw the key and press X to pick it up.