As Katherine grows more in power, the threat seems to multiply and Merlin has no other option but to head home and look for something useful which her parents might leave for her. The magical detector was not there in Harley Merlin 2: Harley Merlin and the Mystery Twins and Harley Merlin 3: Harley Merlin and the Stolen Magicals but now it is complete in this part.
Katherine wants to reach the magical detector, she doesn’t want to see the completion of this device while on the other hand, Harley Merlin wants to reach it first. The entire story is like a race between good and evil, the interaction of the enemies takes place at the climax.