This is the story of John Yesterday who lost his memory.
Slowly he regains his memory and learned what he did during his lost time. These memory snippets are triggered by certain items.
He learned that he lost his memory because he took an overdose of mercury.
He also learned why he lost and was helped to regain his memory.
He also learned that he cannot die and that he became immortal because of a ritual-potion that was performed as punishment 5 centuries ago. He gets killed and starts another life.
The baddies wants to be immortal and the key is to know how John was made immortal. So they killed him with mercury and followed him to know what happened.
At the end, John has to make a choice.