Gnomon by Nick Harkaway.

The book Is set in a near future Britain where surveillance is omnipotent and the accused are interrogated by detectives who read their thoughts.

A suspect dies during an interrogation, highly unusual, so a detective is brought in to investigate the case. She begins to review the thoughts of the suspect and finds not just the suspects memories, but whole other persons whose lives intersect and intertwine created a tapestry narrative that runs counter to reality.

It’s a really Interesting read. I will fully acknowledge its overly long and needed a strong editing pass. But I first read it a decade ago and I still think about it regularly.