On a damp, overcast autumnal day I received some deeply unsettling news. I was to review Indigo Lake, which appeared to be... an iOS first-person shooter.

The horror!

Fortunately, it soon became apparent that developer 3 Cubes Research hasn't thrown another imprecise action game our way. In fact, Indigo Lake can be better described as a free-roaming adventure-puzzler.

Oh, and it's also one of the scariest iOS game ever made.

The weather outside is frightful

If you've ever been unnerved by Japanese horror films such as Ring - or deliberately avoid such films because the very premise spooks you out (guilty) - you'll have an idea of the kind of foreboding atmosphere Indigo Lake malevolently spews out.

It's got a mysterious deserted island (perpetually dark and foggy, naturally), spectral girls with long black hair, ominous hints at a traumatic occurrence, and a spooky soundtrack of groans and creaks that will have you reaching for the light switch.

Indigo Lake is full of familiar scare tactics, then, but that doesn't mean it's any less effective. It's genuinely unsettling, particularly if you plug in a set of headphones.

Not all as it seems

Of course, making an atmospheric and scary game is only half the battle. Fortunately, Indigo Lake is also structurally sound.

It controls like any iOS FPS, but that doesn't pose as much of a problem as you might think. This isn't a fast-paced action game by any stretch of the imagination, and while your primary tool is a pistol it tends to be used to clear planks away and take out health-giving dolls.

Any combat tends to be against solitary apparitions, rather than fast-moving grunts, too.

Indigo Lake works because it's really a slow-paced adventure game, with clues to follow, items to collect and logic puzzles to ponder over. They're not all particularly clever, but with such a thick, gooey atmosphere filling in the cracks it doesn't really matter.

Jeepers creepers

Other noteworthy elements include a 4x4 jeep that can be requisitioned, and like the FPS controls it controls perfectly well within Indigo Lake's carefully constructed world.

There's a novel menu-access system, too, that simply requires you to tilt your iPhone into portrait view. It's clever, though the menus themselves are rather poorly designed.

Oh, and be warned that the game doesn't auto-save. Forcing a manual save system feels more than a little clunky in a modern mobile game.

Overall, though, Indigo Lake's mechanics are simply there to serve its richly spooky universe. Without the palpable sense of dread and foreboding that it engenders, it would probably be half the game it is.

Having created such a deeply unsettling and absorbing world, though, the developer really has nothing to be scared about.