WHAT IT’S ABOUT ABC Family initiates its new name, Freeform, with one of the most ambitious series in its history, based on Cassandra Clare’s YA paranormal/urban/fantasy novel series, “The Mortal Instruments.” Clary Fray (Katherine McNamara) is turning 18, and about to learn she’s a “shadowhunter,” a human/angel hybrid who hunts demons to protect the human — or “mundane” — race. She’s also about to get a little help from her new “hunter” friends, including Jace Wayland (Dominic Sherwood) and Alec Lightwood (Matthew Daddario), as well as her “mundane” BFF, Simon (Alberto Rosende). She’ll need all the help she can get.

MY SAY Fans will probably want to know how this compares with the 2013 movie with Lily Collins as Clary, and Jamie Campbell Bower as Jace. They should be pleased to know — favorably, or mostly favorably. The movie took its own sweet time laying out the story and “mortal cup” mythology. Tuesday’s pilot — which was directed by pedal-to-the-metal executive producer McG, who never took his sweet time doing anything — roars through back story, as the lightsabers swing and the demons dissolve. It’s a mad scramble, occasionally a muddled one, that demands some working knowledge on the viewer’s part.

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But it’s also something of an initiation rite: Like what you see, or at least understand some of what you see, and you’ll likely come back for more.

You will.

McNamara as Clary is good, and also — with her red hair — part of the color palette McG splashes across every scene, especially those inside club Pandemonium, where demons and “mundanes” casually mix, and they all look like they’re on a casting call for “Queen of the Night.” In fact, the sartorial statements easily trump the demonic ones. Special effects are good, occasionally dazzling, rarely scary.

But the fashions? They’re fabulous. Clary starts the episode out dressed like a Brooklyn hipster, ends up attired like Trinity from “The Matrix.” The transformation does her justice.

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BOTTOM LINE Wild start, but a good-looking one. Demands working knowledge of the books.