According to legend the gods used to wrap the Red String of Fate around the ankles of those destined to meet; regardless of time, place, or circumstance.
For Bo to be able to go into Dyson's memory and prove he was innocent of murdering humans and Fae in 1899, and because he was in a remote location, one Red String of Fate was tied around her ankle and another around Dyson's ankle. A third string was tied around the ankle of the Oracle, Cassie, to secure a connection to both of them.
When someone enters another's memory their subconscious stays present, projecting familiar places and people that they know into the other person's past. But if that person inside another's memory does not exit it when they have to, their own memories fuse with the other's and results in clinical insanity. To exit the memory, the person wearing The Red String of Fate has to remove it from the ankle. No one else can do it for them. By removing the string, the person awakens with their mind whole and returned to the present.
The Oracle was there to let Bo know when it was time to exit Dyson's memory.
When the time was right, the Oracle went into Dyson's memory and told Bo to get out of it. The Oracle removed her string and awoke with her mind intact. But Bo did not heed her warning and stayed in it longer.
When Bo did not exit together with the Oracle, Lauren — who tied a Red String of Fate around the ankles of Bo and the Oracle, and had been monitoring Bo's vital signs — tied a string on her own ankle and entered Bo's mind and Dyson's memory to bring Bo out of it. She convinced Bo to leave and Bo took off her string and returned to the present.
But a human cannot enter a Fae's memory and Lauren stayed in it, and Bo could not remove the string from Lauren's ankle. To force Lauren to remove her string and awaken in the present, Bo kissed her.
The red string of fate, also referred to as the red thread of destiny, red thread of fate, and other variants, is an East Asian belief originating from Chinese legend and is also used in Japanese legend. According to this myth, the gods tie a red cord around the ankles of those that are to meet one another in a certain situation or help each other in a certain way. Often, in Japanese culture, it is thought to be tied around the little finger. This magical cord may stretch or tangle, but never break. This myth is similar to the Western concept of soulmates or a destined flame.
- 4.07 La Fae Époque