Learn French: L'intrigue dont tu as parlé manque de suspense. - The plot you spoke about lacks suspense.

In French, the verb to talk about something is parler de. The relative pronoun dont specifically replaces phrases that start with de. Because you are talking about the plot (parler de l'intrigue), you must use dont to connect it to the rest of the sentence, not que.

Since l'intrigue is feminine, shouldn't it be tu as parlée with an extra 'e'?

No, because in the passé composé, you only make the past participle match a direct object that comes before the verb. Dont always replaces an indirect object (because of the built-in de). Therefore, parlé does not change to match l'intrigue.

Why is there a de in manque de suspense?

To say that something "lacks" or "is missing" something else, French uses the verb structure manquer de. The de is a required part of this expression, so you can't just say manque suspense.

Why isn't it manque du suspense? Doesn't suspense need an article?