The Wikipedia Manual of Style/Novels suggests adding information about plot and characters:

Plot

Plot summaries should be concise and an integral part of the article. 400 to 700 words are usually sufficient for a full-length work, although very complex and lengthy novels may need a bit more. Shorter novels and short stories should have shorter summaries.

A plot summary should avoid reproducing the work being discussed. Instead, it should summarise the work, touching on plot, important events, character developments, etc. In a longer work, every conversation and event does not need to be mentioned. Size of the plot summary should be roughly proportional to the size of the plot. This is not always equivalent to the length of the work, since some plots are complex and dense while others are simple and straightforward.

A novel is a primary source for its own plot summary. Citing the novel explicitly in a plot summary section is not necessary provided that the summary is verifiable directly from the plot of the novel itself, that the novel is publicly available, and that its publication details are included within the article, for example in an infobox. Any part of the summary that is not purely descriptive, such as interpretation or explanatory remarks, requires a secondary source.

Plot summaries very often contain spoilers. That is quite normal, and is in line with the spoiler content guidelines and Wikipedia's content disclaimer. Spoilers are no different from any other content and should not be deleted solely because they are spoilers.

Characters

If appropriate, a character section would consist of brief character outlines, as opposed to a simple list. Length of each entry should vary relative to the character's importance to the story. Most articles do not need this section. Instead, a finely crafted plot summary is used to introduce the characters to the reader.

The WikiProject Books/Non-Fiction guide suggests possible structures for autobiographies and biographies:

Synopsis / Summary / Overview / Themes / Plot

• There is no universal set length for a synopsis, though it should not be excessively long. While longer descriptions may appear to provide more data to the reader, a more concise summary may in fact be more informative as it highlights the most important elements.