I seriously can't find the old one, but I'll sum it up again with the improvement:
Essentially the nuclear explosion in Chernobyl, Ukraine had one more "causality" that no one else knew about. It was a science assistant that was supposedly missing and presumed dead. In truth, this assistant was completely transformed from the explosion. The transformation made him into an entity of an unidentified energy that is only detectable on the infrared spectrum. This energy, when in contact with a living being, causes it to be in a various types and amounts of pain. This pain can be anything from a minor headache to the amount of pain associated with breaking literately every bone in their body. They seem to keep a body only in terms of physical appearance while they are incorporeal otherwise.
The person themselves is completely transformed psychologically as well. They seem to possess absolutely no emotions; running only on cold, heartless logic. They only see things scientifically and mathematically. The SCP sees things like the majority of human behavior as illogical and wishes to "correct" that behavior. This drives them to experiment with any person they meet. However, they tend to refrain from using any form of safety precautions. Claiming that they only take away valuable scientific data. They claim that the goal of these experiment as simply to understand human behavior, despite the extreme danger and pain it places it's intended subjects in.