As the Doctor has disappeared and taken his sonic screwdriver with him, you'll need to enter a sequence of digits in order to crack the code that opens the safe. All you have to do is answer questions about places the TARDIS has visited and friends of the Doctor. If you get all three questions right about a single person or place you release a digit and move a step further to opening the safe. But Amy explains all this in the video!
Watch her message and then click on 'Start the History Hunt' to begin the adventure! Initially you'll get a choice of people and places you can investigate. After selecting one of them you should click on the 'Find out more about...' icon. You'll be whisked away to another page where you can either plunge straight into the questions by clicking on 'Unlock a piece of the code' or find out more about the person by following links to websites and exclusive videos. All the answers to the questions can be found in there somewhere!
By correctly answering three questions you'll release a digit that automatically registers on the safe's read out. When you've cracked the code you'll have opened the Doctor's safe and find his favourite painting. And as a sign of the Doctor gratitude for your help you'll get an exclusive short story that fills you in in on what he's been up to whilst you've been helping Amy!
Source: The Publisher Website.