Who are you?

Dirk gets irritated when he receives call from the complete stranger at late night who tells him just trivial things but then he gets to the point: He says that there is a corpse lying in front of Dirk's door. The killer? It is mysterious caller - Dirk immediately concludes. The corpse? Dirk's best friend Dennis. What has this psychopath done to his friend and why? From then on this caller does not leave Dirk no longer alone and drives him almost insane - a bloodthirsty and disturbing madness!