Infinity Ring (Jennifer A Nielsen) Books in Order

Infinity Ring is a multi-author time travel adventure series about fixing history before the future collapses. Its main characters, Dak Smyth, Sera Froste, and Riq Jones, use the Infinity Ring to travel into the past and repair breaks created by a dangerous organization called the SQ.

Jennifer A. Nielsen wrote Behind Enemy Lines, the sixth book in the series. By that point, Dak, Sera, and Riq are already experienced travelers, but the mission is still dangerous. They are kids dropped into moments where one mistake can change more than their own lives.

The larger series mixes science fiction, historical adventure, and puzzle solving. Each book moves to a different period, so the fun comes partly from seeing the same trio adjust to new rules, clothes, politics, languages, and dangers. The time travel setup gives readers a clear goal: find the break, fix the past, and stay ahead of the SQ.

In Behind Enemy Lines, the mission lands in World War II Europe. Dak, Sera, and Riq have to deal with espionage, wartime confusion, and the fact that the Allies' future may depend on a risky deception. The book uses the pressure of spy work well. The characters cannot just charge forward. They have to gather clues, split up, and work in places where being discovered could be deadly.

Because this is book six, it works best after the earlier Infinity Ring titles. The basic adventure is easy to understand, but the relationships, the SQ threat, and the emotional weight of the mission make more sense if readers have followed the trio from the beginning.

Nielsen's contribution fits her usual strengths: quick pacing, young heroes under adult-sized pressure, and history treated as something immediate rather than dusty.

For readers browsing only Jennifer A. Nielsen's books, Behind Enemy Lines is the key title here. For the full story, start the wider series with A Mutiny in Time and follow the numbered order.