Ok I have a theory re the plot

The movie begins directly after Ragnarok, Thanos boards the ship full of Asgardians, Thor battles him but eventually gets his head squeezed, almost to death, but Loki intervenes, begging for his brother's life and offering up the tesseract as compensation. Thanos agrees and throws Thor into space before killing Loki and taking the tesseract. However, he finds he can't get at the space stone inside, so he decides to go to Xandar to break it open using the power stone. Meanwhile, the guardians have arrived at the wreckage where Thor hits their windshield. they bring him inside, and he mentions something that tips Gamora and Nebula off to the fact that Thanos attacked the ship. They track sanctuary II, which is on its way to Xandar and arrive there, where they battle Thanos to protect the power stone, during which Thor tries to destroy the ship. Thanos kills him, which would have the most shock value out of any of the big three (Cap, Tony, and Thor) because few people have theorized about his death and he doesn't fit into the larger MCU all that well without Loki or the Avengers. Thanos takes the power stone, and the Guardians chase him to earth. Meanwhile, Hulk was thrown out of the ship by Thanos as well, and after drifting through space for a while, he lands in Sanctum Sanctorum on earth. Tony arrives, having been alerted to Hulk entering the atmosphere, and arrives to find Wong and Strange standing over a hole where bruce is. Meanwhile, Thanos has arrived, Spidey notices a ship and goes to investigate. Strange, Wong and Stark all exit the sanctum and see it. A heated battle ensues, in which new york is turned to the red wasteland we see in the trailers. The guardians arrive too late to stop the damage, but they help the Avengers escape in the Milano. They split up, some going to Wakanda to get Cap and co, others going to protect the stones. Scarlet Witch and Vision are in hiding, but one of the black order finds them and gouges the mind stone out of vision's head, killing him. He delivers it to Thanos. Meanwhile, another member of the order hunts down Strange. The remaining two attack Wakanda (seeking the soul stone) where several avengers fend them off for a while, (From here on out, this is just wild speculation) until finally being forced to retreat again with the help of the Milano. At this point the Earth is mostly destroyed, and the Avengers seek out the Reality stone as a last resort, knowing it is the most powerful stone and can undo the damage. After a long search, they find it with the Collector, and manage to harness it as a group, like in guardians, and defeat Thanos at last. (There'll probably be more deaths, events might happen in a different order, and there's probably more nuances and twists, but again, this is just a theory.