Your grandfather (Eustace) had been hypnotized and kidnapped by the queen of the black puddle, a sea monster, she kidnapped Eustace with the benefit of eating him in her castle under water. You hated Eustace because he treated you badly but Muriel (your grandmother) loved him very much and did not stop crying and asking for him to come back, so you made the decision to go look for your grandfather, you jumped into a black puddle and swam until you found the queen's castle, there you found Eustace and the monster