Critically-acclaimed adventure game Secret Files: Tunguska is free on App Store until April 20

If you're a fan of point-and-click adventure games, then you have more than a week to pick up one of the little gems that were launched in the mid-2000s, Secret Files: Tunguska.

Developed by German studio Animation Arts and published by Deep Silver, Secret Files: Tunguska has been briefly pulled from the App Store, and it was re-released last week. The good news is the game is now available for free until April 20, after which it will go back up to its full price.

Tunguska is the first title in the Secret Files series, which comprises three more games: Puritas Cordis, Secret Files 3 and Sam Peters. For the time being, Tunguska and Sam Peter are the only Secret Files games that are available for free on the App Store.

The Secret Files saga follows the adventures of Nina, an attractive young lady who sets off to look for clues relating to her father's whereabouts, and Max Gruber, a young colleague of her father who offers his help.

Secret Files: Tunguska offers the full experience of a point-and-click adventure title, so there are no episodes that you'll have to buy after finishing the game. Obviously, you'll have to look for the other Secret Files games if you want to learn more about Nina and Max's adventures around the world.