Effective horror films these days are harder and harder to come by, and it all depends on what you want from the genre.

In Insidious, Saw and Paranormal Activity creators Wan and Whannell appear to have collected together all their favourite horror elements from scary classics – namely Poltergeist, The Amityville Horror and The Shining – but not forgotten to add a good dose of humour, with nods to Beetlejuice and even Ghostbusters. It’s a strange but fixating mish-mash of ghoulish behaviour, but it’s also one of the most effective, jump-out-of-your-skin and hilarious creations out in recent years.

At first Renai Lambert (Rose Byrne) can’t understand why things move around in her new home, or why the baby monitor starts whispering evil nothings to her. Then her adventurous son, Dalton (Ty Simpkins), ventures up into the creepy old attic, falls off a rickety old ladder, and doesn’t wake up the next morning. The doctors are baffled and so is her husband, Josh (Patrick Wilson). They must find the reason why their child is comatosed – and quick. But they don’t have too long to wait for answers when paranormal activity kicks off in the house, and someone keeps making bloody paw prints on Dalton’s sheets. It seems evil spirits are trapping their kid in a realm called The Further, and they must go and rescue him before it’s too late.

What starts out like a creepy Paranormal Activity copycat – minus the videotaping – turns into a totally unpredictable other-worldly journey that not only freaks the living daylights out of you, but has you giggling like a maniac. The latter is simply down to Wan and Whannell following the golden rule of not creating a horror that takes itself too seriously, with Insidious becoming a parody in itself. But don’t think that because the film ‘borrows’ from others that you’ve seen it all before because there is a nice little twist that turns proceedings into some sort of latter-day fairground or theatrical show, and gives a bizarre explanation for all the spiritual phenomenon. Hell, there’s even a Spidey impression by a demon that looks suspiciously like Darth Maul.

This is the key to Insidious; keep you guessing, engaged and entertained. As horrors go, it might not be very dark in nature – even when freaky-looking Barbara Hershey as Mom comes to visit and talks in riddles, but it knows how to set up the jumps well that still catch you off guard at times. Admittedly, there are parts that play out too long, but others are gleefully plan crazy, such as the competitive comedy double act by medium Elise Rainer’s (Lin Shaye, the wrinkly lady from There’s Something About Mary) ghostbusting sidekicks Specks (Whannell) and Tucker (Angus Sampson), plus Madame Rainer’s gasmask appearance that’s like experiencing a weird acid trip.

The film also ticks the ‘good-looking cast’ box with Wilson and Byrne in the leads, who give as good as they get in trying to protect their young family from spirits dashing from room to room, as well as violently convulsing structures. It’s a family and their young boy at stake, so the outcome has got to be a happy and resolved one – or has it?

Scared? You bet. Entertained? Totally. Insidious comes from accomplished filmmakers who know their genre and what presses the fear and funny buttons. This reviewer would now love to see Wan and Whannell tackle a seriously scary film based on its ‘explanation’ in question – thinking an adaptation of James Herbert’s Nobody True… Not sure about Insidious invoking childhood fears of darkness and demonic nightmares, as some have commented, but baby monitors are definitely the scariest and most evil things ever invented.