Walk-in (concept)
A walk-in is a New Age concept of a person whose original soul has departed their body and has been replaced with a new, different, soul. It can also refer to a soul without a human body that enters a body with a soul, with the two souls subsequently sharing that one body. An example of this is the concept of twin flames. If one dies, they may return to share the body alongside their living twin. Ruth Montgomery popularized the concept in her 1979 book Strangers Among Us.