Goosebumps My Best Friend Is Invisible Book 57

Sammy Jacobs is into ghosts and science fiction. Not exactly the smartest hobby, at least not if you ask Sammy's parents. They're research scientists and only believe in real science but now Sammy's met someone who is really unreal. He's hanging out in Sammy's room and eating his cereal at breakfast. Sammy's got to find a way to get rid of his new 'friend'. The only problem is that Sammy's new friend is invisible.