The Water Castle by Megan Frazer Blakemore

All things are impossible until they are discovered. Ephraim and his family travel to a small town to help his father recover from a stroke. His father hasn't spoken or moved on his own since the attack, and Ephraim just wants him to get better. The strange house was built by a family ancestor who was searching for the Fountain of Youth. Ephraim's new classmates are all much smarter than himself, and his brother sets a new pool record the first time he gets in the water. Then, the house seems to hum at night leading up to a huge flash of blue light in the sky. Weird. Ephraim and two new friends explore tunnels located under the house, and the truth about his relative's experiments start to emerge.

The plot was a mixture of science and magic. Actually, the second half of the book reminded me of Tuck Everlasting as the author explored the possibility of eternal life. You won't find any action in the plot, but it unfolded like a mystery. The families of the three main characters had decades of history behind them, and Will hated Ephraim, a lot, for quite awhile. I didn't expect them to join together in search of the truth. Mallory's mother was rarely seen, but she had an unusual story, if you put the clues together.