Learn Turkish: Bizi izleyen ajan çok tehlikeli. - The agent following us is very dangerous.

The suffix -(y)An is a participle that turns a verb into an adjective describing who or what is doing the action. Here, it is added to izle (to follow/watch). Since izle ends in a vowel, it takes the buffer -y-. İzleyen ajan literally means "the following agent" or "the agent who follows."

Why is it bizi instead of just biz?

Even though izleyen is acting like an adjective to describe the agent, it is still a verb at its core (izlemek) and needs a direct object. Because "us" is the specific target being followed, you must use the accusative form bizi.

How is the word tehlikeli formed?

It is built from the root noun tehlike, which means "danger." The suffix -li means "with" or "having." So, tehlikeli literally means "with danger," which we translate as "dangerous."

Where is the word for "is" at the end of the sentence?

In Turkish, the "to be" verb for "is" or "are" is often simply implied by the word order, without needing a suffix. You could add the formal copula suffix -dir to make it tehlikelidir (sounding more like an objective fact or a formal statement), but in everyday speech, leaving it off is completely natural.