With “Wildcard,” the sequel to “Warcross,” author Marie Lu fulfills her unspoken promise to readers to keep the action and the tech fast and furious, just like the action in the fictional game of Warcross. The sequel takes the reader forward, but also lets the reader visit the past.

In the first book, Emika Chan comes from nowhere (New York) and ends up in Japan keeping company with Hideo Tanaka, the creator of the NeuroLink, a world that people fitted with special lenses can see and which is a technology that changes life as we know it. Instead of looking at your phone for directions, virtual grids create lines on the road that you can just follow. You can link with people and visit them virtually. There’s lots more futuristic technology, some of which this reviewer frankly didn’t quite understand, and that’s okay. There’s lots more in this book to enjoy and appreciate.

Hideo’s life and creations have had one purpose: to find Sasuke, his younger brother who had been kidnapped as a young child. He felt guilty as they had been playing in the park and he turned around, and his brother was gone, never to be seen again. In this sequel, the reader gets to find out what happened to Sasuke,

At the end of the first book, Emi finds out that Hideo has created an algorithm for his new lenses that will allow him to control people’s thoughts enough to ensure that no one commits crimes. He is determined that no one be able to kidnap another child or commit a murder, and if he has to take away a bit of free will, the end justifies the means.

Emi doesn’t agree. And this book raises some very interesting and complex ideas about right and wrong, and whether it is okay to use technology to control people. In fact, in light of the last presidential elections, one might wonder if that is already happening, albeit not exactly in the manner shown in the story.

A huge answered question is the identity of Zero, the mysterious figure from the first book, and the group of “Blackcoats” he works with. Are they the antidote to Hideo’s plot? Are they worse? Who can Emi trust?

And with Lu’s fabulous writing, her clever dialogue, her descriptions of a fantastic Japan as seen through the NeuroLink, and Emi’s relationship with Hideo, the reader will fly through the book. Emi’s dilemmas ring true, and she isn’t infallible. And that all just makes the reader like her more. The ending is lovely, with a little mystery that could just turn into a future book, although Lu says that this is a duology, and it’s done.

Please note: This review is based on the final, hardcover book provided by Putnam, the publisher, for review purposes.