In the fourth book of the Alien Next Door series, Halloween is just around the corner, and Harris is excited to share the holiday with Zeke, who doesn't even need a costume! Harris is ready for Halloween and is very excited when he sees Zeke's "costume," which is just his true alien form. Harris is sure Zeke will win the costume contest at school! Zeke also uses his powers to help Harris make the best costume he's ever had, but Roxy feels left out, as she and Harris usually make costumes together every year.

On Halloween, one of the other kids at school is jealous of Zeke's amazing costume and plots to sabotage it. Will Harris and Roxy be able to stop him and help Zeke win the costume contest?