The Far Realm itself may be inaccessible and inhospitable, but psychic entities reach into mortal dreams and power leaks across where the planar boundaries are thin. The grimoires of mad cultists find their way into the larger knowledge pool, and spells that should not have come to light wriggle forth. However, there are also some spells available to fight such entities within, giving a grim glimmer of hope that the fell entities might be sealed away from the Material Plane once more.
Many of the spells within work best in the hands of a Dungeon Master / Storyteller, but the player characters might just dive down the rabbit hole when they investigate their quarry too closely. Just remember, no matter how grim things may get...
...you can always make a new character.
- from the publisher's blurb