Redemption at Gontranno is the final level of Hitman 2: Silent Assassin. The only objective is to kill Sergei Zavorotko and his bodyguards. Stealth isn't really an option in this level.
Kill Zavorotko
Run to the garden shed and grab an SMG. A few people should have followed you; kill them and kill the sniper on top of the ruins. Shoot any remaining guards outside and go inside. Kill the guards in the entrance hall and go upstairs. Kill a nearby sniper and grab his custom rifle, then pick off the rest of the snipers. Once only Sergei is left and there is a cutscene, go to the balcony that's on the left when facing the confession booth and shoot the heart in it. Sergei will be hit and will run out onto the middle balcony, where you can just see the top of his head. Shoot him to complete the game.
Custom Rifle
Finish the level with it in your possession, select "Start Game", then "Current Game", start any level and save.
Chronology
St. Petersburg Revisited - Redemption at Gontranno - Hitman: Contracts - Asylum Aftermath