The fourth book in the CAHILLS VS. VESPERS series, the follow up to the worldwide bestseller THE 39 CLUES. After pulling some spectacular heists, Amy and Dan have become two of Interpol's most wanted criminals. So when Vesper One orders them to steal the world's largest diamond, they know they're facing life in prison . . . or worse. But with the Cahill hostages still in peril, Amy and Dan have no choice but to launch a mission that leads them to an ancient city full of dangerous secrets. With a Vesper mole sabotaging the Madrigals from inside, Amy and Dan have to fulfill their enemy's request before it's too late. Vesper One has developed a taste for killing Cahills, and Amy and Dan aren't going to wait to see who's next.

Targeted by Interpol after a series of spectacular heists, a reluctant Amy and Dan are ordered by Vesper One to steal the world's largest diamond, a demand that is challenged by their efforts to rescue the Cahill hostages and stop a Vesper mole.

The president's daughter has been kidnapped by the elusive and lethal Ghost Cell. Quest (Q) and Angela are in hot pursuit with vicious winds and blinding rain thwarting them at every turn. It's a desperate high stakes chase. But who is chasing whom? Are Q and Angela the hunters or the hunted?

With the nation reeling from the recent terrorist attacks, Q and Angela leave Chicago and arrive in San Francisco. Their parents are determined to continue the Match tour but for safety's sake, they have decided to send Q and Angela to boarding school. Not happy at the thought of being taken off the trail of the ghost cell, Q and Angela race against time with Boone and the SOS team to find Number One, the leader of the world's most feared terrorist organization. It's the final showdown.

After Q and Angela help foil a Ghost Cell plot in San Antonio, they head to Chicago, the next stop on the Match tour. Since they've been busy fighting international terrorism, they're behind on their school assignments. Their parents tell them if they don't get caught up, it's off to boarding school. But who can concentrate on homework when there is a mystery to solve and international terrorism to thwart? Angela is obsessed with finding out more about the mysterious Boone. Q is more interested in not going to boarding school. But when Boone and his SOS crew are ambushed on their way to Chicago, it becomes abundantly clear. Someone inside their inner circle is feeding the Ghost Cell information. As they dig ever deeper to learn the identity of the mole, Angela and Q uncover the Ghost Cell's next plot. And it's much, much worse than a car bomb. They plan to unleash a chemical weapon over the skies of Chicago. And it's up to Angela and Q, along with Boone and Croc, to stop them.

Fresh off a "too close" encounter with the terrorist group, the Ghost Cell, in Kitty Hawk, North Carolina, Q and Angela head to San Antonio, Texas. As their parents' band, Match, prepares for a concert at the Alamo, the two discover that the Ghost Cell has its tentacles everywhere, including the Lone Star State. With each passing hour, Q and Angela uncover more clues and discover more leads. And the mysterious Boone and his SOS group leave them with more questions than answers, for there is much more to Boone than meets the eye. With time running out to stop another Ghost Cell attack, Angela and Q and the others begin to wonder. Are they following the Ghost Cell or is the Ghost Cell following them?

Serious games provide a unique opportunity to engage students more fully than traditional teaching approaches. Understanding the best way to utilize games and play in an educational setting is imperative for effectual learning in the twenty-first century. Gamification: Concepts, Methodologies, Tools, and Applications investigates the use of games in education, both inside and outside of the classroom, and how this field once thought to be detrimental to student learning can be used to augment more formal models. This four-volume reference work is a premier source for educators, administrators, software designers, and all stakeholders in all levels of education.