Simple concept as a pathway to an alternate dimension, think the wardrobe or platform 9 and 3/4…
Around the world, ATMs of a shadowy bank (Rothschilds…) implement a new biometric security system, the Indigo Hand. It is simply a hand scanner built into the machine, glowing indigo, where you place your hand for verification.
It will only work for people who are part of the trial run, and seemingly nobody is. Even so, a rumour started that says certain random or special people can be transported to another place and time by placing their hand there.
The rumor is true, but impossible to prove. People are transported, but no matter how long their journey is, they will always be returned to the same place and time, so that bystanders notice nothing other than you placing your hand there, and removing it.
It is by nature an individual experience that nobody with you can join in on.
Experiences are so random that all seem implausible. Attention seekers lie that they had the experience, latching onto more desirable themes.
By the law of averages, one instance of multiple people from the same friend group, somewhere in the world, all have the experience. They trust each other enough to share what they encountered and work to solve what it really is.
That’s the framework. The otherside can be anything. I like the idea of not being able to prove your encounter, like UFO witnesses.