Well if you want a spoiler here it is for the final boss.
He is a military captain that had charge of cleaning up the santa cabeza mess and he missed some because it got out, so they were called in again to once again clean up the mess.
In the overtime mode you are told to get the items to stop franks zombification, along with 10 queens, when you do so isabella temporarily cures you, no one knows if the cure is permanent or not, but since the ending opened it for a sequel i doubt it.
Anyways, she says she can make a anti pheromone that will repel the zombies, the problem is it comes from a spray can and it is a little aura so you have to hold isabellas hand through a tunnel with more zombies then the matienence tunnel. Get to the end of this however and you have to fight a prototype tank, a fairly easy fight, however once you beat it a man known as Brock pops out, putting the tank on manual control and knocking your hummer on its side, forcing frank out with a tank barrel down his face.
The general tells you all about the infestation of the wasps how it all happened etc, then he turns around saying But it isn't over,wouldn't you say? Frank jumps up and punches him knocking his cigar out of his mouth.
This however is where the hell begins, any healing items you had, any weapons you had they all disappear, you have to fight this guy ontop of a tank with hundreds of zombies below u with nothing but unarmed, personally i used the summersault kick, very damaging and it stuns if you get him off guard, but you can fight him however you want, just know that if you die you go through the tunnel exit again, the tank, then him again, kind of a burden but the infiniti mode is worth it.
The book to make blades go longer for is known as the criminal biography in the back of sir book alot, in wonderland plaza.