I would suggest taking out the first sentence. It is generic and doesn't tell me anything about Joseph, secrets or murders. The last two sentences also seem generic without tellling me, again, why 17 yo is uniquely qualified for investigative work (he has clairvoyance? is very smart? or?) or the kind of dreadfull secrest that lead to the murder spree. Is there a suicide pact? Cult? Is it supernatural war? Mafia is moving onto the new territory?
The blurb doesn't need to hide things, it needs to entice people to buy-in. If it is sufficiently intriguing, people would want to get more. Otherwise it's like buying a cat inside a bag, you don't know what you are paying for, even though you may hear a mew.