Brainchild is a fantastic new YA book, filled with intrigue, drama, and fun. It's a perfect introduction to the YA genre and was a really enjoyable read.

What worked:
Isobel and Carl are brilliant twins who live alone after their father’s death. Their father’s assistance becomes their guardian, but she ends up moving out to live with her boyfriend. Carl’s mind can create amazing inventions, including a gadget to help free a classmate from the school bully. Carl has no tolerance for bullies. Isobel is more sensible and is the voice of reason. As the synopsis says, an evil half-brain is stolen and implanted into a teenage boy. The twins do something not often seen in middle-grade novels; they enlist help from adults and the authorities. They immediately go to the prime minister of England and share the story of the evil brain.
The story obviously pits good versus evil. The teen with the evil brain, Rufus, kills random people, but there must be a purpose behind his violence. The twins convince the prime minister of their father’s experiments and become integral parts of the reaction plan. The plot evolves into a mystery, as they uncover how the half-brain was stolen and the future’s further evil plans. The author provides significant twists and surprises when Isobel and Carl learn about an unseen, devious scheme unfolding. Readers may be surprised to learn there will be a sequel.
A decision is made to implant the good half-brain into a teenager, Spike, but it’s four years earlier than the father recommended. The good and evil brains stimulate other abilities that are unforeseen. Super intelligence is not a surprise, but enhanced speed and strength emerge too. Spike becomes a main character, so readers will experience more of his abilities as the need arises. Some chapters periodically share Rufus’s evil actions, but they usually involve smashing things or killing someone. Readers discover that other anonymous characters are working with him, and their identities and motives are added to the mystery.
What didn’t work as well:
The hardest things to accept are the characters’ superior physical abilities. There’s no mention of them being part of the brain experiments, and the author doesn’t offer much of an explanation. Implanting the two half-brains four years early may be a reason, but there’s no scientific basis for it.
The final verdict:
The evil brother’s violence makes this book more appropriate for more mature middle-grade readers. The conflict’s seriousness and the mystery behind it create a suspenseful, exciting story. I recommend you give this book a shot.