I think the series makes Mr Sutton seem very weird. I'm sorry but I think the actor is really not a good cast. In the books Graham Sutton is just 23 years old and Lydia is 18/19. Graham just finished university and it's his first year as a teacher now. So their age gap really is just 4 or 5 years. But in the film series Graham looks like he is in his middle 30s or maybe almost 30. That's why his and Lydia's relationship looks so weird here. I wish they had casted a much younger actor for him because in the books there is really chemistry between these two and they are actually really cute together. :)
