During the scorching summer of 2011 in bustling central Madrid, in the background of the imminent Papal visit, the metropolis pulsates with anticipation while thousands of pilgrims flock to the capital. However, something sinister is going on in the bowels of the city: a string of sex-related homicides have been taking place under the police's noses, nurturing a scandal that no one wants to break out. Under those circumstances, two investigators, the brilliant, yet eccentric Luis Velarde and the hot-headed loose cannon Javier Alfaro, must track down the sadistic, methodical serial killer in total secrecy. But to catch a killer, one must first keep his own demons at bay.