Learn Italian: Nessuno ha scoperto le loro vere identità. - Nobody discovered their true identities.

Nouns ending in an accented vowel, like identità, are invariable. This means they keep the exact same form in the plural. To know if they are singular or plural, you have to look at the words around them. Here, the feminine plural article le and the plural adjective vere show us that it means "identities", not "identity".

Why isn't there a non in this sentence to make it negative?

In Italian, when a negative subject like nessuno (nobody/no one) comes right before the verb, you do not use non. You only use double negatives if the negative word comes after the verb (for example: Non ha scoperto nessuno, meaning "He hasn't discovered anybody").

Why is there an article (le) before loro?

Loro is the possessive adjective for "their". In Italian, possessives almost always need a definite article before them. While loro is an exception in that it never changes its ending to match the noun, the article before it still must agree. We use le to match the feminine plural identità.

What is the infinitive verb for scoperto?