Kayla and Mishalla are GENs, genetically engineered non-humans. Unlike other people who were born to mothers naturally, Kayla and Mishalla were gestated in a tank. Not even considered human by the trueborns (upper-class natural-borns) and lowborns (lower-class natural-borns), GENs are created for a specific Assignment, which they take at age 15 and from then on are treated as slaves. All GENs are marked with a tattoo on the side of their face upon creation, which serves a dual purpose of making them recognizable to non-GENs as well as being used as a sort of electrical conduit to upload information to their brains.

Kayla and Mishalla are close friends and almost sisters. They were raised together and turned 15 at around the same time, with Mishalla leaving to take her Assignment a little before Kayla. Mishalla serves as a caretaker for trueborn children in a sort of nursery and Kayla serves as the attendant to Zul Manel, the bed-ridden patriarch of a very wealthy and influential trueborn family.

The book alternates between their perspectives, but most attention is given to Kayla. Kayla has been told her entire life that she is worthless, good only for the one thing she has been Assigned, so much of the book is necessarily Kayla’s path to realizing her own self-worth. She’s an interesting character who experiences a lot of growth, and her story (involving the secrets kept by the trueborn family she serves and by extension secrets kept by her world at large) is fascinating. Mishalla is a bit flatter, but I liked her story as well – the children she cares for are disappearing in the middle of the night, spirited away by her trueborn keeper and never seen again. About halfway through the book, Kayla’s and Mishalla’s stories intertwine.

I loved so much about Tankborn. Sandler has created a unique society (set on an entirely new planet called Loka) ruled by a strict caste system: trueborns at the top, lowborns at the bottom, and GENs beneath even them. What’s more, the trueborns themselves are divided into castes. The ideal skin color is what most would consider medium-brown. The farther away from this color a person’s skin deviates (darker AND lighter), the lower they are on the totem pole. (Kayla’s skin is light brown and Mishalla’s is pale white, so even if they were trueborn, they would both be low trueborns.) It’s a unique take on the caste systems in our own past and present worlds, and Sandler makes it believable.

I loved the plot of Tankborn. That’s a fairly simplistic statement to make, but it’s a true one. As a seasoned SF reader, I thought I knew where Sandler was heading with the story, but she surprised me multiple times. The biggest twist was something I never saw coming, but it wasn’t a cheat since I could look back and see the groundwork Sandler had laid for it the entire book. There are a couple of love interests for our two lead females, but they’re among the weaker aspects, although they are sweet.

Tankborn is a science fiction story for readers who like science fiction. What I mean by that is Tankborn most likely won’t hold the interest of casual science fiction readers. Sandler’s world-building is complex, involving a string of new vocabulary, complicated social structures, a completely new religion, and a giant backstory that unfolds over the course of the book. It’s necessary for the reader to understand all of this world-building to comprehend the story, and it’s too easy for casual SF readers to give up when they stumble across yet another unfamiliar element. Readers who enjoy SF naturally, though, will relish this aspect.

I think the length of my review is a good indication of how complicated this story can be, but that makes it wonderful for readers who want to get lost in another world. There are so few YA books out there that are wholly, unabashedly science fiction. Most YA SF books I come across are set in our world with a twist, and while I enjoy those, they’re not my original love.