Gregorio and Manuel were best friends. They both had a tattoo of a night buffalo, which Gregorio insisted was done with the same needle, so their blood would mingle. Since Manuel started sleeping with Gregorio's girlfriend, the friendship had become increasingly difficult to live with. In the aftermath of Gregorio's suicide Manuel struggles to get his life back on track. Everyone seems to suspect him of knowing more than he lets on and everyone seems to be keeping their own secrets, including his girlfriend. Most disturbingly Gregorio appears to still be watching him, letters from him appear through the post, containing enigmatic messages, 'You won't be able to run from the night buffalo', they promise. Gregorio hadn't finished dying yet. From the acclaimed writer of "Amores Perros" and "21 Grams", this is the story of a passionate and destructive menage a trois and the tricks your mind can play on you.