As the cover might imply, there's a ton of spectacle and high adventure. It's a mystery/adventure/quest story that involves vampires, monsters, automatons, airships, magical artifacts, you name it. It mixes actual history (it's set in Victorian Britain) with the fantasy/horrors of that day. Bram Stoker might actually exist, but so might his creation, Count Dracula, and other vampires. And I prefer not to say much more about this.
Anyway, our hero is a young, earnest fisherman from a village called Sandsend. His father's disappearance (and rumored death) start the plot, as young Gideon is certain that foul play is behind the situation and does what any loving son would do; attempts to contact the hero of the penny dreadful stories he enjoys reading: the dashing Capt. Lucien Trigger. Gideon, who's about 25 or so, is described as being muscular and broad shouldered, but to me, what came across far more in the writing was his earnestness, vulnerability and wide-eyed wonder. I kept trying to picture him as a strapping, muscular lad, but the image of Andrew Garfield wouldn't leave my mind. Despite that, having reviewed the choice, I think Aaron Taylor-Johnson would fit much better. Kick-Ass showed that he has the same vulnerability but is a much more impressive physical specimen.
Stoker's take on the supernatural changes dramatically when he meets - not Dracula, but Dracula's widow, the Blood Countess, Elizabeth Bathory. I'm less worried about historical accuracy when casting Bathory, because we really have no idea what she looked like, only paintings, which may or may not be accurate. All we need is a beautiful woman who also looks dangerous. Eva Green, anyone?
After getting separated from Stoker, Gideon's adventure takes him to Einstein's house. Well, not Albert. Albert's grandfather. Among the wonders there is a beautiful automaton (the titular mechanical girl) who looks almost perfectly like a young lady, who begs Gideon to take her with him. He agrees. She looks very young, innocent and blonde. Kinda like Sophie Turner.
They need to go to Alexandria, it turns out, and hire local sub captain Mr. Okoth. Who better to play a large, intimidating, but ultimately jolly African man? Adewale Akkinuoye-Agbage, of course!