This novel is hard SF/adventure and was published by Solaris on October 15, 2019. It is #2 in the series, following The Quantum Magician, and runs 300 pages. This review contains major spoilers.

The Scarecrow shares the information he’s gathered on Belarius Arjona and his involvement in the recent Sub-Saharan Union’s rebellion and attack on the Congregate. In response, the Congregate defies the Banks and the Plutocracy and nukes the Garret, asteroid home of 4000 bioengineered Homo quantus. Arjona and Cassie Mejia are doing research on the wormhole system from their new inflation racer The Calculated Risk. The AI St. Matthew interrupts to let them know about the problem, and Arjona and Mejia make a plan to use the stolen time gates in the hold of The Calculated Risk to go back in time and rescue the population from the Garret. They lease and refit freighters, take them back in time and rescue everyone in the Garret that will leave with them. Homo quantus has been considered a failed genetic experiment, but suddenly their military potential is apparent, and the Scarecrow reclassifies them as bioweapons. Arjona and Mejia decide they need to hide the Homo quantus somewhere in their expanded wormhole system where they won’t be found. But their research on it isn’t complete—they need historical data in order to calibrate their model and plot courses. Arjona approaches Lieutenant-General Rudo and Colonel Ayen Iekanjika of the Union with a plan to go back in time and collect data from the planetoid Nyanga, offering the location of unknown wormholes in the Union’s Bachwezi system in trade. Rudo and Iekanjika are angry that Arjona stole their time gates, but Rudo agrees anyway. The Scarecrow is hot on their trail. Can Arjona, St. Matthew and Iekanjika obtain the data they need and successfully return without creating a paradox and changing the timeline of history?

This summary is a massive over-simplification, of course. As in The Quantum Magician, Künsken’s strong suit here is the science, all projected and highly plausible. The author comes up with entertaining applications; for example, where Cassie leads the Scarecrow on a chase through the multiple dimensions of a wormhole, and then doubles back for an inspired and unconventional attack. The entertaining Homo eridanus Stills is back for this installment, cursing in several languages as he brokers Arjona’s deal and then serves as the pilot to Nyanga-in-the-past. Most of the drama in the story falls on Iekanjika, who has to figure out the politics of the Union in its early days and decide what to do about causality in the timeline, while Arjona wanders off, stressing about a quantum intelligence on the planetoid that’s fated for extinction. Nobody is especially happy with each other by the end of this, so I’m expecting the story will continue as they work out their issues.

I had a few complaints about The Quantum Magician, but Künsken has fixed most of those issues here. There’s no real hook for the story, just an argument at the beginning, but the action line goes up sharply when the Congregate ship fires on the Garret, and it remains pretty gripping the rest of the way through. This is strongly plotted, the characters are fairly well-rounded and it’s strongly diverse. Künsken presents the ever-interesting Stills to fill the mid-novel slump some authors experience, and things get pretty intense as Iekanjika realizes the truth about the people she’s dealing with on Nyanga. I also have a fair idea what Bel and Cassie look like at this point, though I still didn’t get a good description. They’re bioengineered from Afro-Columbian stock, so have dark skin, hair and eyes. Arjona isn’t black enough to pass for the Shona stock of the Union, though, and has to darken his skin to pass. Besides that, Stills calls him “fancypants,” from which everyone will have to draw their own conclusions.

Highly recommended, especially for science geeks.

Five stars.