It revolves around Pathaan (Khan), an ex-armyman turned undercover agent who gets caught on a mission. He has now returned to save his country from a former R&AW agent Jim (Abraham) who has turned rogue after he was wronged by his own people. The film introduces its characters with solid backstories. An ex-ISI agent, Rubia (Padukone) becomes a part of the mission and has her loyalties questioned at several junctures. And that's pretty much about it.
The whys and hows get answered in the due course of time with a lot of in-your-face action and hopping from one picturesque location to another with views that sometimes distract from the actual action unfolding in front of you.

You've seen Khan do Chaiyya Chaiyaa on top of a train, but Pathaan gives you much more. He's fighting on top of a Hummer, then somewhere mid-air on a rope tied between two helicopters, and then jumps onto a truck. Basically, there's very little action on the ground and you'd see men in Pathaan mostly flying through the most high-octane action sequences.
Also, when you have Khan and Abraham fighting it off on the big screen, you don't really need anything else to boost that adrenaline. And yes, the train isn't forgotten. Perhaps, the best and highest point of the film is when Pathaan meets Tiger (Salman Khan) and the two have quite an elaborate action sequence inside and then on top of a moving train. It was hard to focus on what was happening on screen with loud cheering, hooting, screaming, and whistling throughout this scene. It was nothing short of celebrating true stardom with two superstars being in one frame in their best possible avatars