When does homage become plagiarism?
I've often found that Terry writes homages to other book and films in his stories, but I don't see them as plagiarism.
For example: I've often thought that some of the plot of Mort is an homage to Dickens's 'Great Expectations', with Mort playing a sort of reverse Pip. And Death as a sort of anti-Miss Haversham character.
In Great Expectations, Miss H employs Pip in a needless task essentially so that her ward, Estella can learn to be cruel to a male of her own age (as part of Miss H's revenge on men). Death on the other hand employs Mort to pointlessly learn to be his apprentice while his real motive is to give companionship to Ysabelle of a male of her (sort of) age.
I could be totally wrong about that - but if I'm right, I would call that Terry stealing a plot from Dickens.