There is no such percentage but the work on prima facie viewing should not disclose major similarities between them ruling out the possibility of coincidence

When determining whether or not someone has committed copyright infringement, the courts use a test known as substantial similarity. However, deciding whether a work is substantially similar is neither clear-cut nor precise. There is no exact formula, but there are standards the court can use to reach a decision.

Looking at how much of a new work is similar to an original work can help a court decide whether the use is trivial or warrants further examination. If only one sentence from a 300-page book is copied, the court would most likely not find that use to be substantial. On the other hand, if one line of a four-line poem is used, there might be an argument that a significant amount of the original work was copied.

The second part of substantial similarity is the similarity element. The actual creative composition has to be similar, not just the idea. Ideas cannot be copyrighted, nor can facts, processes, ingredients, and other such information. A poem about spring flowers is an idea—and not a unique one at that. But the exact word choice, order, punctuation, and even sentence length are all unique creative aspects of the original work. So a court must compare the two works to see if the new one so closely resembles the original that it was likely copied. If the average person would confuse the new work with the original work, then there is a strong likelihood that a court would arrive at the same conclusion.

if substantial similarity is found then you will definitely win. You would have to consult a lawyer a do a meeting to tel properly how much work is used and then proceed.

Infringement include reproduction.

What is relevant to consider to constitute reproduction is stated below.

There must be a sufficient degree of similarity between the two work and some casual connection between the two.

Where there is a substantial degree of objective similarity this will afford prima facie evidence of casual connection between the two works.

Where there is a parody or burlesque,the test to be applied is the writer has bestowed such mental labour upon the material taken and had subjected it to such revision and alteration as to produce an original work.

The most crucial part of infringement of copyright in making film from a book or other film is the use of the characters or dramatic incidents of that original work. If there is such use in the film then it is clearly a copying of the original work.

This is very much a glaring instances of copyright violations for which you need to file a suit for injunction

Through the suit you can seek both damages, credit in the start cast and further relief depending upon the details of the dispute.

For taking this forward you may feel free to  get in touch..

If the evidence shows that there are striking similarities between
the two works, that the plaintiff's was the earlier in time and that the
defendant had the opportunity to get to know the plaintiff's work, then
a court may well find copying proved in the absence of any convincing
explanation to the contrary by the defendant."

2) o "the question whether the defendant has
copied a substantial part depends much more on the quality than the
quantity of what he has taken".

For copyright infringement, % of similarity dose calculate but use of any copyrighted work without the permission of the owner. Copying part of the artistic work which another has copyright, amounts to infringement

Substantial similarity in copyright infringement. To win a claim of copyright infringement in civil or criminal court, a plaintiff must show he or she owns a valid copyright, the defendant actually copied the work, and the level of copying amounts to misappropriation.

Many courts also use "substantial similarity" in place of "probative" or "striking similarity" to describe the level of similarity necessary to prove that copying has occurred.

Under the doctrine of substantial similarity, a work can be found to infringe copyright even if the wording of text has been changed or visual or audible elements are altered

Direct evidence of actual copying by a defendant rarely exists, so plaintiffs must often resort to indirectly proving copying. Typically, this is done by first showing that the defendant had access to the plaintiff's work and that the degree of similarity between the two works is so striking or substantial that the similarity could only have been caused by copying, and not, for example, through "coincidence, independent creation, or a prior common source". Some courts also use "probative similarity" to describe this standard. This inquiry is a question of fact determined by a jury.

While actionable infringement is more likely to be found where greater levels of similarity exist, substantial similarity has also been found where the portion copied was small but constituted the "heart" of the work.

In determining whether use is substantial, courts look not only at the proportion of duplication in comparison to the relative size of the works, but also to such considerations as the creativity of the copied material, its use in both works and its centrality to either

Hi

There is not percentage limitation in many kind of copyright issues.

Just initiate the complaint. 

The story and incidents mentioned in your novel should be similar to the movie. The overall effect of the movie is to be seen whether a reasonable person after seeing the movie comes to a conclusion that the movie was in fact a copy of the novel.

Sir in the court there is formula no fixed percentage for seeing copyright violation court sees that if there is substantial reproduction of plaintiff work without permission then the relief is granted.

you have a prima facie case of copyright
infringement in your story.You may approach district court for restraining publication of movie.

1. There is no such percentage is set up as mark for violation of copyright.

2. If prima facie evidence shows major similarities in the work then it will be clear violation of copyright infringement and you can send legal notice to production team of movie.