ntrigues is a uncountable noun. No "s" is countable noun.
Please correct me if I'm wrong.
You are not correct in this case where I think of "intrigue" as an uncountable like "money".
For example, consider the following:
"There is intrigue in ever part of the company. The workers are plotting against the management. The management is trying to subvert the actions of the workers. This is an unhealthy place to work!"
This is how a native English speaker would normally write these sentences.
Yes, you can add an "s" and make it plural. But in this case you would be talking about situations that were not related.
Consider this example:
Intrigues have been a part of history, since Adam was a child.
In this case, one intrigue does not relate to another and there are many of them. However, I still think the sentence written this way is still fine.
Intrigue has been a part of history, since Adam was a child.
You can ask if there is a difference between these sentences. I would say the first sentence is considering many individual acts of mystery or devious plans. The second sentence is addressing the concept of "mystery and devious plans" in general.
In the case of the original post, I think "Mary" is looking at the atmosphere in general, not individual acts.
