Word for telling about events of a movie/book etc

Solution 1:

This isn't a single word, but phrase give away works.

TheFreeDictionary defines give away as:

To reveal or make known, often accidentally.

It can be used for movies, such as the phrase "gave away the ending". There are a lot of examples of that on Google.

Solution 2:

Before spoiler, people would actually use the word reveal.

Whilst being a verb. it can also be used as a noun, as in the big reveal, such as with a magic show.

verb make (previously unknown or secret information) known to others.

noun (in a film or television programme) a final revelation of information that has previously been kept from the characters or viewers.

Alternatively, you could use unveil

verb show or announce publicly for the first time.

Definitions from Oxford Dictionary

Both work in the context that you've described:

He revealed an object

He unveiled an object

Solution 3:

I like divulge:

verb

[WITH OBJECT]
Make known (private or sensitive information):

ODO