The Dreamwalkers are generally regarded as a mere myth, a bedtime story for children. They are supposedly a collection of vagabonds and castaways who, lacking any real place to belong to in the waking world, have found their purpose in dreams.
Like all legends, this one bears a grain of truth.

The Dreamwalkers do indeed exist, though they are quite different from how the childrens tales depict them. For starters, they come from all walks of life, not simply street urchins, however romanticized. They also can’t flit in and out of some otherworld of dreams at will, nor can they see into a persons soul. To describe what they can do, it’s best to describe how they find each other.

It starts when someone has a dream. It may be about something that they lost, the actions of someone that they were unaware of or something as simple as what somebody says. Seemingly an innocent dream, it later is proved to be true. The dream led them to the item that they lost, to discover the cheating of their significant other or someone says what they had dreamed, every intonation and stutter exactly the same.
From there, most simply write the event off as coincidence. A few, however, become interested. They begin to try and trigger these dreams as they fall asleep, and gradually find that they can cause them and even direct them. They begin to be able to seek out bits of information, and even watch the actions of others before they come to pass. A few stay at this stage, but at some point, most direct their efforts to seeing if their are any more like them.
In this, they find a bit of a surprise.
Hidden in taverns, basements and ruins across the continent there are pockets of those like them. And wherever they look, they find one word, inscribed on objects over and over: Freinakt.
Dwarven for "free night", this is the password to the safehouses that are hidden throughout civilization. When said to a dreamwalker, they will act as though it means nothing. However, when next the one seeking them out sleeps, they receive a dream. It directs them to the nearest safehouse, where they then recite a very specific (and unique) phrase. They are admitted, and their new life as a Dreamwalker begins.

Now having access to actual instruction and explanation, they no longer need to feel out their abilities as though they were crawling through shadow. They learn that they can project dreams to others, they can take control of their own dreams to previously (pardon the pun) undreamed of extents, and even change the behavior of others over time.
They are mostly left to their own devices, the only real requirements being to record any new dreaming abilities or the like that they may discover. At times though, they actually do receive a form of assignment. Usually something along the lines of ‘make sure the baron doesn’t go into his wine cellar’ or ‘find the tablet detailing the battle of Tarras Hadrain’.
There are ranks of a sort, though they are hazy at best. At the lower levels, it mostly dictates who takes orders from whom. The highest levels, however, are aware of much more than one would guess, and actually are guiding many of the activities of the group.
Unknown to all but the leaders of the organization, they aren’t the first incarnation of the Dreamwalkers. The current order was founded a couple of hundred years ago by one with the ability to direct his dreams. He discovered a series of stone tablets, quite ancient, that told of an order that had mastered the same abilities that he found he possessed. Though the tablets told him much, they stopped somewhat abruptly.
He was ecstatic to later find another such tablet, almost halfway around the world. It described more of the order, including secrets of controlling dreams. It was then that he decided to see if there were others, for finding all of the tablets was beyond what he could accomplish in his lifetime. There were no easy ways to find others, it was looking for the proverbial needle in the haystack. Over time though, he found a number of them, or they found him. Together, they were the first of the current incarnation of the Dreamwalkers.
Today, they seek out more tablets and other artefacts from the lost culture of dreamers. With each tablet, their collective abilities mature, and a number of trinkets have also been recovered that allow the few privileged enough to use them additional dream based abilities.

Hooks

-Recently, there was a large series of thefts from a nobles manor during a soiree. The peculiar part is that he was having this event to show off his collection of peculiar archeological finds, and only the ones that seemed to be from a similar but unidentified culture have gone missing. Nobody suspicious was seen, and only those invited were allowed in. The mystery only deepens when one of the objects is found in one of the attendee’s homes.
The objects were fragments of a shattered artefact from the ancient culture that was the seed of the Dreamwalkers, and knowing that they would be here the Dreamwalkers manipulated the dreams of most of the attendees so that, when there, they would work together to take the objects. Due to the work of an exceptionally talented dreamwalker, the actual actions of theft have actually been erased from the minds of those involved. All that’s left now is to recover the one piece that happened to escape…

-The PCs find an ancient tablet while investigating a ruin. That night, before they’ve managed to liquidate it, they all share a strange dream, instructing them to bring the tablet to a specific place.
Could it be that the Dreamwalkers have just found field agents?