Angela's Aliens — Janet Taylor Lisle

When their best friend changes drastically, the Investigators suspect extraterrestrial trouble

Georgina and Poco should not be climbing an apple tree in the dark. But Poco, who talks to animals, has recently developed a serious crush on a robin, and she gets worried when the bird doesn't return to his nest one night. Poco convinces her friend to come with her to check on the nest, and while they're peering through the tree branches, they see strange glowing objects in the sky. The array of lights can only mean one thing: aliens.

The next morning, Poco's robin returns and, more importantly, so does Angela. Angela had been the girls' best friend before moving to Mexico a year ago, but she comes back totally changed. Before, she was short, chatty, and imaginative. Now she is tall, sullen, and cold. When Georgina reminds her of their former club, the Investigators of the Unknown, Angela shrugs her off. Poco and Georgina realize that the aliens have claimed their first victim, and they will have to move fast to save their friend.