Once downloaded, there's no signup or login screen; you just tell the game your name and you're instantly thrust into the action. Your otherwise nameless character receives a plea for help from Thomas Horgan, a disgraced former great detective currently in exile. After a period of stalling, you answer his call and set off to the grim, far-flung town of Snowport, only to discover him brutally murdered.

As you're under suspicion for Horgan's murder, you must prove your innocence by solving his last case. That means battling the rogue gallery of Snowport's locals, plus the machinations of both the Royal Society and a dangerous cult that lurks in the shadows. It's the sort of delicious gothic horror that I have something of a soft spot for, and one that ensured I kept playing.

As for the game's mechanics, Snowport itself is a map with key locations -- your lodgings, the police station, tavern, etc. -- all highlighted. Getting between them requires the burning of actual shoe leather, as your steps, as monitored by the phone, are counted. You need to walk between 300 and 500 steps to reach most of the locations, where you then interview suspects or search for clues.

The interviews are of the traditional, branching style you find in many RPGs: Say the right thing at the right time and you'll be rewarded. Say the wrong thing and the suspects and witnesses soon turn hostile and ask you to leave. At specific points, you'll be able to switch into AR mode to hunt for clues around your local location. Then it's off to the next building, a few hundred steps away.

Most of the game can be played at a leisurely pace, but there are certain moments where you're given a deadline. These challenges are either related to important side quests that help you complete the entire chapter or are used to build tension toward the climax. The deadlines aren't particularly taxing -- five minutes to walk 100 steps or 20 to walk 500 -- but they mean you can't put the game down even, for instance, if your lunch break has ended.

If you want to play the game without the walking, either due to indolence or bad weather, you can skip it by calling for a cab. You're given one for free at the start of the game, with additional rides setting you back £1.99 ($2.56) for 12 or £2.99 ($3.80) for 30. Subsequent chapters, of which there are four, will set you back a further £2.65 ($3.40) per time. As the first part of the game is free, the overall price you'll pay is around £8 / $10.

Silent Streets has plenty of things going for it, including a well-written and intriguing story, beautiful hand-drawn artwork and good voice acting. But its game mechanics feel less like a way to make the story more immersive and more like a way of stretching out what little content there is. Without the walking -- which I do enjoy, especially as motivation to get me out of the house -- the chapter would last half an hour, tops.

There are a couple of other glitches that the studio will need to work out, including app crashes if you pick the "wrong" option at a key moment in the game. But that's a small issue -- and it helped me avoid ruining the ending by picking the wrong culprit.