End of the Line

I've done all I can, hiding the beast away,
but with fang and claw,
I will rend my prey.
Limb from limb, with a mighty roar
blood-caked face, teeth mired with gore.
On a manic mission for your life,
no comfort for you, heart filled with strife.
You shouldn't have bothered, should have left me be; an eye for an eye and you will see!
You prodded on and on,
in spite of my pleas, you're human cancer,
a walking disease; Knock! Knock! Here comes the plague doctor.
You've failed the test, and I'm your proctor!
You've reached final payments, and it's time for your dues, and here's something else you probably knew. You can't take it with you,
no matter what's said on the pulpit;
Lucky for me, you can't run faster than a bullet.