Luca has an older brother Mateo(voiced by Tress MacNeille) that he hasn't met before during the weekend, Luca's mother Daniella pulls him aside and tells him the truth of having an older brother and how she felt overprotective of him too. Surprised at this, Luca vows to know who is brother is what happens when an unexpected sea monster comes to the surface? How will Alberto and Giulia react?