Into the Gauntlet begins as Amy and Dan Cahill enter a London hotel tired and with no lead whatsoever.

The other teams follow them there, but they are forced to work together as they make their way through the gauntlet, a series of doors with questions about the clue hunt.

However, every door except the last is opened, and when they reach the vial that supposedly has the master serum, they find that Isabel Kabra beat them to it.

After finding their way out of the gauntlet, the teams separate on amiable terms, and Amy and Dan stay behind with Fiske Cahill and Mr. McIntyre, who give them a letter from Grace.

Amy and Dan are left in the legal custody of both their Great-Uncle Fiske and Nellie, but the letter makes it clear that their adventures aren't over yet.