Animorphs

Jake's great-grandfather has died. It blows the family away--especially Jake's mom. So Jake's parents decide they should all travel to the great-grandfather's home to help with any arrangements. In another state. For three or four days. This is a very big problem for Jake's brother, Tom. He can't be away from the Yeerk pool for that long. So Tom refuses to go--and his father insists. But Tom's Yeerk will do anything to survive. Including making his father less of a problem. Now Jake, the other Animorphs, and Ax have to find a way to protect his father without Tom discovering their secret. And without having to choose between his father's life.... and Tom's.

The conspiracy
1999
Scholastic