On each episode, three teams of two contestants apiece answer questions to accumulate prize money, which is placed into a large safe in the studio.
Contestants may buzz-in at any time, but must answer based only on whatever information the host has read to that point.
The host asks one question to each team, starting with the one that brought less money through from Round 1.
Each correct answer allows the team to either add £10,000 to the safe or expand their "window of opportunity" to open it by one second.
The team can accumulate up to £40,000 in this round by answering every question correctly and taking the money on each.
Each teammate is given a button that controls one of the two still-closed locks on the safe, and a partition is placed between them to prevent any communication.
Both teammates must continue the countdown in their heads; once they believe it has reached zero, they must push their buttons within the length of their window of opportunity to open the locks.