Playing as Anna in the game, you need to solve the mystery of real events. By solving interactive puzzles, you'll use your in-game phone to browse through information and find new clues to what happened. Here's the story description on the Steam page:
The Riese Project – Prologue is a playable guide to the full version of the game... As Anna, you will follow your grandfather's discoveries and unravel the mysteries of World War II. Fight for the truth and risk losing your way back to reality. Experience a captivating world that completely captivates the player.
"The Riese Project – Prologue" is now on SteamVR for $14.99. A release date for the full version has yet to be determined.