خلاصه داستان : باند Mystery Inc. باید Coolsville را از حمله هیولاهای گذشته خود نجات دهد که توسط یک شخصیت شیطانی نقابدار در تلاش برای از بین بردن باند زنده شده است.

After solving their last mystery at Spooky Island, the Mystery Inc. gang is back in Coolsville, where they are being honored with their very own exhibit at the Coolsonian Criminology Museum. However, when a masked villain steals costumes of classic monsters on display and brings them to life, the gang must come out of retirement to solve the case.