These are definitely YA books. The main protagonist is a 14 YO London young male of Indian ancestry. He is a math, physics, and computer genius, and completes his father's work on the device that will allow easy exploration of all 10^80 alternate Earths, rather than just the 10 parallel Earths currently known.
The central cast of characters is the 5 person crew of a freight airship from Earth 3 - an earth with coal, electricity, carbon nanotubes, and 200 meter long airships, but no oil and plastic. So kind of a steampunkish feel. The characters are all quirky. Kind of reminded me of "The Expanse". The crew of a small ship makes for a manageable number of characters with quirks and backstories, I guess.
The plots move quickly. A few twists seem arbitrary, but, that must be the price you have to pay for an airship duel. McDonald comes up with very interesting alternate histories for the parallel earths, and seemed to be just getting warmed up. At the end of the 3rd book, we've taken care of the local crises but still have the overarching bad guys (The Order) to be dealt with. McDonald could probably crank out 1 of these stories every year or so without breaking a sweat.
Bonus points for having a Tarot-like deck of cards as part of the plot. The origin of the deck is unknown, and it is a dynamic deck, with cards being created and removed by its keeper, the 13 YO female main protagonist and (puppy) love interest. Some good card names:
- The Cockle-child
- Swannhilde and Swannhamme
- The Winter Watcher
- The Traveller Hasteth in the Evening
- Season of the Wolf
- Two Bad Cats
- Lone Tree Hill
- The Sun Empress
I'm down to 21 unread books in my iPad. I may be forced to read something worthwhile before too long. Oops.