Just what is the mood of the book. Several times I've been disappointed when what I thought was going to be a funny story suddenly turned dark or even the reverse. Or what started out suspensful turned into a bit of melodrama of the worst kind.
How does one maintain a not of humor, drama or even melodrama when the scene could be very different, It's a matter of word choice.
When developing the mood or tone of a story there is form. Comedy, Drama, melodrama.
Then comes atmosphere. The writer can choose light or dark.
There are hundreds of emotions the writer wants to bring to the reader. Laughter, poignancy, threat. More than I care to name.
The fourth is expression - masculine (just the facts) or feminine (using description.
The one thing about mood is sustaining the one the writer has chosen throughout the book. The answer lies in word choice and showing, not telling.