The day after spring break Susan’s teacher Ms. Schwartz went missing, their new sub Mr. Smith is very strange. After school Susan follows Mr. Smith home. She finds out that Mr. Smith’s real name is Broxholm and he is an alien. The next day Peter and Susan sneak in to Mr. Smith’s house, again. They find Ms. Schwartz in the attic in a column of blue light. Ms. Schwartz could talk to them through telepathy, and told Susan and Peter Broxholm was planning to steal the best, worst, and three most average kids on march twenty sixth. They tried to take pictures of the column and print it at the drug store. But they could only see the column of light and not Ms. Schwartz. At the night of the Spring concert Susan played her piccolo in front of Mr. Smith. A few seconds later the whole band mainly made of sixth graders started to join in. They played like their life depended on it. They got Mr. Smith to take off his mask. Suddenly, Peter ran out of a door and ran away with Broxholm. When the police and Susan arrived at Broxholm’s house, Peter and Broxholm were already heading of in an UFO.

The main character in the story is Susan. She is brave because she went into Broxholm’s house three or four times. She is also very determined because she is determined to unmask Mr. Smith.