Silas Sinister is one of the main antagonists in Return to Halloweentown. He is the richest and most powerful warlock in Halloweentown, father of Sapphire, Saige and Scarlet Sinister and the leader of the Dominion, an evil organization that wants to rule Halloweentown.
Silas Sinister is the current leader of the Dominion. He and his family were also part of that powerful coven for generations. He and the rest of his fellow high-ranking members are waiting for the chance to take over Halloweentown forever.
That time has come when the heroic witch Marnie Piper learned the secrets of her family's hidden royal linage connected with Queen Spendora Cromwell and the founding of Halloweentown and returned in time from the past to retrieve the Gift, her family heriloom which is the most dangerously powerful amulet because its power of mind control can corrupt evene those who wielded it. Chancellor Goodwin steals the Gift for the Dominion and the Sinisters, in order to use it to take over Halloweentown. Knowing that only a Cromwell can use the Gift, the Sinister Sisters (working with the Dominion) transform Dylan into a dog to compel Marnie to comply with their demands. If the Sinisters and the Dominion don't turn him back, he will stay that way forever after Halloween passes. They agree to return him to his natural form if Marnie controls Halloweentown for them. While it seems that she has agreed to aid them in their heinous plot, she is really fooling them, and turns on them once her brother is released from the dog transformation spell.
That night during Halloweentown's 1000 years anniversary, the Dominion came with the crowned Marnie under their control as they prepare to use the Gift's mystic power to control all of Halloweentown forever but her mother Gwen and her brother Dylan use their combined to not only free Marnie but to stop the Dominion's plans as well. The Dominion, having been discovered for the evil ones that they are, attempt an escape, but are apprehended by none other than Professor Periwinkle who was revealed to be an undercover detective of the Halloweentown Anti-Dominion League. She imprisons them in a Witch's Glass where she has stripped them of their magic and arrested them for treason.