[1] The story picks up right after the previous book and continues to follow Dan and Amy as they try to get back the kidnapped members of their family as they go on a journey to remember.

The book starts with Dan and Amy Cahill, the two main characters, at a train station in Florence.

The two hide there until they reach the next station at Engelberg, where they run away and call the Cahill Command Center in Attleboro.

Realizing that they should start at the auction in which the De Virga was last seen, Ian Kabra tells them how to dress like they fit in at once.

After dressing up, Dan and Amy go to the auction, where they sneak into the record room and start searching for clues.

After sneaking out of the auction house, Dan and Amy meet McIntyre, who tells them that it is unsafe to remain in Lucerne.

During this time Dan and Amy explore the castle for clues they find another code and Casper Wyoming.

Hamilton shows the group a lead that suggests going to The Library of Philosophy and Cosmology in Prague.

The two start a fire to take Dan and Amy out by using the library's halon gas, which removes oxygen from the air.