Complex sentence: The film's opening sequence was not in the previous film "Scars of Dracula", but is completely new and sets a new short series of the Hammer Horror Dracula chronology finishing in the following film "The Satanic Rites of Dracula".
Split into simpler sentences: The film's opening sequence was not in the previous film "Scars of Dracula", but is completely new and sets a new short series of the Hammer Horror Dracula chronology up to this point. This series ends in the following film "The Satanic Rites of Dracula".