Dee Dee's imaginary friend comes to life and annoys Dexter. Dexter ends up wishing him away, then he realizes he made a terrible mistake.

Koosy tells Dee Dee that he is the king of the land of Koos, but when Dee Dee goes there...

Dexter and Koosy must save Peepers, otherwise the whole land of Koz will disappear.

Dexter, Monkey, The Justice Freinds, Dee-Dee, her imaginary freind Coosie, Mandark, his parents, and Dexter's Parents participate in a cross-country race