He, at the beginning of the film, is recruited to investigate Tenet, an inversion of time which is being manufactured (sort of) by Sator (played by Kenneth Branagh,) a Russian, given instructions from the future to end the world.
With me so far?
It turns out, however, the Protagonist is at the beginning of his time journey, and starts to meet people along the way who he has in fact recruited in the future, such as Robert Pattinson’s Neil, who in turn brings on a whole host of mates such as Aaron Taylor Johnson’s Cockney sergeant.
First, the Protagonist heads to Mumbai to track down the arms dealer Priya (Dimple Kapadia), who tells him of Sator’s plutonium discoveries as a child and how he is the man to look for with regards inversion.
Soon, it becomes clear Sator is a nasty piece of work, having blackmailed his wife (Elizabeth Debicki) to stay with him after she accidentally sold him a forged painting, and is keeping her child as a kind of emotional hostage.