When posties start turning into werewolves and solicitors into zombies with their skulls hanging out, policeman Nick thinks he's going mad, writes Sian Brewis.

He's not. He's one of the last of the Grimms, demon hunters born to fight creatures that go bump in the night. If you're thinking Buffy at this point, you'd be spot on.

Grimm (Watch, 9pm) is Buffy creator Joss Whedon's latest fantasy series and – whisper it – shows promising signs of being as good as early Slayer episodes.

It was packed full of superior chills and thrills. The special effects were incredible – people going from normal to gruesome in the blink of an eye, and it didn't stint on the horror.

There were plenty of moments to make you jump and the writing, too, held up well. The plot was coherent, fun and packed a lot into 40 minutes.

Even if the whole moment when Nick learned he was a descendent of the Brothers Grimm was a bit clichéd, there's enough here to keep you wanting to watch.

This is the twisted side of fairytales – witches shoving kids into ovens after fattening them up and bears probably taking horrible revenge on Goldilocks.

Oh, and it may be a very good idea to stay well away from woods. Ever.

Heading into it all is Nick and his partner Hank. Their jail cells seem packed to the rafters with demons in human form which only Nick can see.

Nick's Giles is his cancer-stricken Aunt Marie. A former librarian, she travels around in an Airstream trailer packed with books on demons and a weapons closet that looks like a medieval torture chamber.

The only other person he finds who can help is Monroe, a werewolf who has reformed thanks to the power of regular Pilates classes.

After a blood-curdling start in which a jogger with a red hood is torn to shreds in the woods by a werewolf, the race is on to save a girl who had the misfortune to head out to her grandfather's house in a coat with a red hood.

The culprit turns out to be a mild-mannered postal worker, who wears pastel yellow jumpers and does needlepoint on his cushions.

There's lots to admire here and, hopefully, it won't fall into that whole introspective teen angst thing which just gets so tiresome.

From fantasy to reality in America's Serial Killer (Channel 4, 10pm) a horrifying story of a man who has been secretly killing and dumping prostitutes for years. Relatives of the victims and suspected victims were a grim combination of loss and bewilderment, and the police – who ignored reports of missing women from relatives – didn't come out of it particularly well.