The book Mary gives Fergal for his birthday is "Titus Alone", the concluding volume in the 'Gormenghast' trilogy by Mervyn Peake. In the book, Titus, the heir to the castle of Gormenghast, decides voluntarily to cut himself off from his ancestral home and not to claim his heritage; rather like the choice which Mary is expecting Fergal to make in the film.
This movie features 4 Game of Thrones (2011) actors, including Kate Dickie (Mary), Daniel Portman (Paul), James Cosmo (Laird) and Ian Whyte (Beast). Each of them respectively play Lysa Arryn, Podrick Payne, Jeor Mormont and Wun Wun.
One or two smaller roles were offered to hired extras, such as Christopher Downie (Police Officer #1), as a way to stay on budget.