My favourite book and how I'd cast it for a movie

 I've decided to go a little off-piste for this topic from Long and Short Reviews, as I was struggling to think of a favourite book of mine that hasn't already been made into a film. My automatic response when I like a film is to check out the book. So I decided to do this with my favourite of my own books, because I would love to be able to cast it for a film.

Photograph has one particular trick in that the two heroines are fraternal twin sisters - as written, Tara and Azure are facially identical but have opposite colouring. As a result, I would prefer to cast one actress in a dual role and have her wear wigs and coloured contact lenses. My favourite actress for this role would be Katharine Isabelle, who I've loved in every film I've seen her in.

For Tara's love interest Ryan, I would cast Taron Egerton. Ryan is American, but I'm pretty sure Taron Egerton could manage an accent. I loved him in the Kingsman films and also Rocketman.

For one of the side characters, Tara's roommate Kiki, I always saw Kirsten Dunst. She's possibly a little old for the role now but I don't believe I ever stated Kiki's age, so I don't think that would matter.

The most difficult character to cast would be Liam, Azure's husband, who is a celebrity theme park owner and was originally inspired by Gene Wilder's performance as Willy Wonka. I eventually settled on Benedict Cumberbatch. He's very good at playing genius characters.

So which book would you like to cast for a movie?