|Men of Letters
|Transports demons and monsters
| 1.01 Pilot (The Winchesters)
1.02 Teach Your Children Well
1.03 You're Lost Little Girl
1.08 Hang On to Your Life
1.13 Hey, That’s No Way to Say Goodbye
Six points of infinite light. The order must be right. To capture the darkness and the light.
– N/A, 1.01 Pilot (The Winchesters)
The Ostium is a "monster trap" that was built by the Men of Letters, it is adorned with various runes and powered by dark magic. The box is activated by the tracing of the runes in a precise order, once opened the box can trap demons, monsters and the Akrida. Originally it was believed the Ostium was capable of killing the Akrida, but was later revealed that the box was designed to transport rather than kill. According to Henry Winchester, the Ostium's power source determines where the portal opens. With the Akrida, a piece of rock from their home universe was needed to power the Ostium and send them back.
The Ostium can be used in reverse to bring something back to its world by feeding it an object connected to that person and pressing the symbols in reverse. However, reversing the Ostium's polarity can only be done at midnight. When used in this manner, the Ostium glows red instead of blue and shoots a red light into the sky. The thing that is summoned by the Ostium then appears close by rather than just emerging from the box.
Overuse can break the Ostium as happened when Samuel Campbell used it to banish multiple Akrida at once. However, it can be fixed by physically repairing the box, although this takes quite some effort and time.
After being repaired by Millie Winchester, the top and sides of the box are covered in metal, presumably used to hold the pieces together.
While under attack by zombies, Lata attempts to use the box against them, but it fails to work for some reason.
The Monster Box is still powerless and the group searches for the partner of the demon that had possessed Ada in the hopes of finding out more information about it.
Lata mentions that despite all of their research, the Monster Club still can't get the box to work again.
With the help of her son, Ada finds more information about the box in an abandoned Men of Letters office in Ann Arbor, Michigan. The notes prove to have been written by Henry Winchester and reveal that the box is actually called the Ostium. Rather than killing monsters, it banishes them from this plane of existence. In addition, the Akrida are all linked to their queen so banishing her would kill all of the rest. The Monster Club performs a seance to summon Henry's ghost who reveals that the box's power source determines where the portal will go. Henry directs John to a piece of the power source that he was given in case of an emergency which proves to be a rock from the Akrida's home universe. By placing it on top of the box, the group is finally able to recharge it.
In a final confrontation with Rockin' Roxy, Mary succeeds in using the Ostium to banish the Akrida leader, leaving behind Roxy's unconscious body. However, this fails to affect the other Akrida, revealing that Roxy wasn't actually their queen. As John and Mary are cornered by several Akrida, an injured Samuel uses the Ostium to banish them all.
It's revealed that using the Ostium on Roxy and the other Akrida broke it and Ada is working on finding another magical solution. With Samuel's permission, Millie takes the Ostium home with her and attempts to repair it.
Millie mentions that she's had no luck so far in fixing the Ostium. In addition, it's revealed that Rockin' Roxy and the other human hosts of the banished Akrida survived their possession and exorcism by the Ostium.
Jack Wilcox reveals that, shortly before his retirement 15 years before, the Akrida had tried to invade, but the Men of Letters pushed them back to their own world using the Ostium at the cost of the Men of Letters suffering severe casualties. However, some of the Akrida remained hidden on Earth, including the Akrida Queen.
After Joan Hopkins, who is the Akrida Queen, banishes Dean Winchester and the Impala through a portal that will tear them to shreds, the Monster Club comes up with the idea of using the Ostium in reverse to bring Dean back. At midnight, Mary, Millie and Lata feed the Ostium Dean's Journal and push the symbols in reverse. While the Impala appears nearby, Dean doesn't, causing the group to summarize that Dean must be dead. However, this proves to be enough to defeat the Akrida as the Impala, not being of their world, is able to kill Joan. After emerging from Joan's portal, Dean explains that he was trapped in the world between the worlds, but as Dean is already dead, it couldn't harm him.