Beings from a different world could attack at any minute
the beings want one of two things: his power so they can take over their world or his death so he canít stop them.
First, referring to them as "beings" makes it seem like you don't even know what you're dealing with. What are they?
Second, the idea is presented in such a lackluster and familiar manner as to be the storyline for any number of books we've already read, movies we've already seen. What makes yours different? What's special about it? This letter reads like you're trying to keep a secret from the agent - the real storyline - and that's a mistake. Fess up. What is your book about?