This is a blend of film and book elements from Prince Caspian and Voyage of the Dawn Treader. The title is from a quote by Dante Alighieri: "Remember tonight ... for it is the beginning of always."
How do you define the beginning?
Looking back, Edmund finds it difficult to tell where he and Caspian begin.
There's the time in Aslan's How, after the Witch, when Caspian sees him as him for the first time and not one of the Kings of Old or Peter's little brother. Remembering the look on Caspian's face then, a mixture of guilt and something Edmund still cannot define, can send shivers down him that have nothing to do with the cold.
Or there's the time Caspian kisses him after events at Narrowhaven, frantic and desperate, needing to prove Edmund's survival to his own satisfaction and confirm Pug and his cronies have done him no lasting harm. There have been hundreds of kisses since then, but Edmund will never forget that first one: messy, rushed, but perfect.
It is perhaps inevitable the two become lovers before the Dawn Treader even leaves the Lone Islands; this too is a beginning of sorts. Edmund hadn't dreamed hands and mouths and bodies could bring so much pleasure; that it's with someone he loves makes it even more overwhelming.
How, he wonders, is it possible to define their beginning if it's impossible to imagine their end?