[POSSIBLE SPOILERS] All known story details so far.
TFW2005 collected information from various publications about the movie: http://news.tfw2005.com/2016/12/06/transformers-last-knight-plot-roundup-329777
-Opening scene will explain TF mythology.share
-Megatron & Optimus backstory, Quintessions and Primes will be explored.
-Optimus will question his leadership and there will be a new prime.
-Cade is on the run and is hiding the Autobots from TRF in the junkyard in South Dakota.
– Isabela lost her family in Chicago and is with Sqweeks since then.
-Sqweeks is broken, can’t transform, and can only say ‘chihuahua’.
-Tessa is in hiding and will be explained in the film.
-TRF is led by Santos (Santiago Cabrera).
-Laura Haddock plays Vivian Wembley and her family is tied with the macguffin of the movie.
-Hot Rod has a French accent and he has two vehicle modes; lambo and citroen ds (Vivian’s car)
-Anthony Hopkins plays Sir Edmound Burton.
-There’ll be a new villain, a different form of a decepticon.
-There will be a submarine TF.
-Grimlock will be in the beginning of the movie, he’ll have a larger role but not much.
-Mini t-rexes who just started to breathe fire.
-There will be hints to other spinoff movies.
-There won’t be any female transformers in the film.
-Cogman is a headmaster.
-Decepticon bike and VW van are called ‘Mohawk’ and ‘Hooligan’.
-An Autobot was going to get killed by military by accident.
-Bumblebee movie script doesn’t have a lot of other TFs, but it may change.