The first downloadable expansion for this spring's celebrated Xbox 360 horror game Alan Wake arrives next week. It's called The Signal, and it's a mystery.

The official description of The Signal indicates that our writer-hero Alan Wake continues to be "ravaged by dark forces" as he longs for his wife. "In 'The Signal,' Alan finds himself facing a threat unlike anything he has encountered before –- and yet, the nightmarish mysteries feel intimately familiar for our favorite writer... His only hope for survival lies with the mysterious Diver, Thomas Zane."

What's it all mean?

Here is a teaser video:

The Signal, which was created by the Alan Wake team at Remedy Entertainment, will be available for download on Tuesday, July 27. Newly-bought copies of the Alan Wake game include a code that will grant players access to The Signal for no extra cost. People who have the game but lack the redemption code will be able to buy The Signal from the Xbox Live Marketplace. An Xbox spokesperson wasn't able to give us the price by the writing of this post, but if we find out, we'll let you know.

Microsoft describes The Signal as the first game add-on for Alan Wake and prices it at 560 Microsoft Points. We have no information about when the next one will be out or what it's about.

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