To avenge his mentor?s murder, an assassin who turned his back on the intelligence world returns, discovers he?s no longer the hunter, but the hunted and has to stop them before they destroy the core principles of the countries founders.

A solid improvement over your first draft. And Foxtrot25s redraft is a further improvement. Though,?I am having difficulty seeing how solving the government problem relates to avenging his mentor's murder? Was his mentor involved in preserving the integrity of the country?

remove "turned his back on the Intelligence world" How does one do that? He can quit working for the government. Hunter, hunted mentioned in the same line sounds weird too.

To avenge his mentor's murder, a former assassin must take down the shadow government he used to work for before they destroy the integrity of the country.