Up until recently, the seven sins ruled over all the mortal desires. They escaped the wrath of the angels by signing a pact with Lucifer. However, this contract must be renewed every 666 years. The angels, aware of this, prepared an ambush at the moment right before a new one was ratified. Suspecting foul play, Lucifer swears revenge on the sins and together with Archangel Michael imprisons them deep into the bowels of Hell. The seven sins must now find a way to escape and take over the world again.
Party of Sin is a side-scrolling action platformer with an emphasis on puzzle-solving. The player controls one of the seven sins at a time, but can always switch to another without impediments. Every sin has one melee attack and one special skill. The special skills are most often used when dealing with puzzles, which actually require the sins to combine their efforts. The sins have the following special skills: Envy can shoot laser beams, which makes her the only character that can go into ranged combat with the enemies; Gluttony can eat objects and spew them in another place (this includes enemies as well, which may be completely consumed after some time has passed); Greed has a grapple hook which allows him to reach higher places, activate switches and bring enemies into melee combat; Lust can seduce and stun enemies, as well as create cloud platforms, where possible; Pride's sword dash allows him to do additional damage and jump farther, while his normal melee attack can deflect missiles; Sloth uses her teddy to slow down objects and enemies; Wrath's bull rush can push heavy things and break through wooden walls.
In the single-player mode, the sins go through a series of levels, unlocking them one by one. While the main objective is to simply reach the other end of the level in order to finish it, this may actually involve solving several puzzles and defeating waves of enemies along the way. During the fights, the sins will lose some of their health, which may lead to death. The life bar is replenished by eating red apples. There are also green apples scattered around the levels, albeit in places harder to reach. If these are collected, they can be spent in the shop in exchange for different upgrades to the sins' abilities. Party of Sin features a cooperative mode as well.