In Guilty Party you play as a member of the Dickens Detective Agency, which is led by the Commodore. The Commodore is planning on retiring, but when his arch-nemesis, the master criminal named Mr. Valentine, learns that the Commodore is retiring he begins his ultimate crime spree and kidnaps the Commodore's wife. It's up to the Dickens Detective Agency to put a stop to Mr. Valentine. The game proceeds in turns where the player moves through a board game-like setting.
The gameplay revolves around each player having a set amount of tokens (or actions) per turn and having to find enough clues before the guilty party can escape. The gameplay is turn based and can be played solo, cooperatively or competitively. Each action the player takes, such as moving into another room, questioning a suspect or looking for clues wherever a question mark is displayed uses up one token. Once all tokens have been spent the next player's or the guilty party's turn begins. Whenever the player decides to perform an action other than moving from room to room they will be prompted with a mini-game. The objective of each is to fill up a meter by performing the mini-game correctly and once the meter is full the player will receive a clue, either a witness testimony or a written note for his journal. Each one of these clues contains a sentence that can scanned with a lie detector to determine whether it is true or not (displayed in red or green). Using these the player can build a profile of the suspect and eventually narrow it down by comparing his profile with that of the people on location. Once ready to make an accusation, the player will have 3 opportunities to make his case against the suspect. If the game is in story mode the investigation will result in a cutscene revealing the guilty party's motives and the game will move on onto the next level.
Tokens are small golden coins embossed with a T that the player collects. Each time a player performs an action such as moving to a different room, inspecting a clue or interrogating a suspect a coin is spent and disappears from the players total. Each turn the player is given 4 tokens but can gain more through Savvy cards or clicking on certain objects in the environment to find hidden coins, allowing them to take more actions per turn.
Savvy cards are collectable cards that can be played during your turn during a case, and are drawn at the beginning of each turn (or at any time at the cost of 1 token). There are a total of 50 different cards with both positive (for your character) or negative effects (for other players in party mode), from unlocking doors locked by Mr Valentine to calling a suspect to the room you are currently in. Several cards are more powerful versions of other cards. For example, 'Open Room' allows you to unlock all the doors in a room of your choice, whereas the locksmith card unlocks every door in the crime scene. Savvy cards can be found hidden in the environment by clicking on objects in the background.
There are a number of awards/accolades/achievements that can be earned through gameplay called badges. These are obtained by performing well during mini-games and completing various tasks in the games story and other modes. At the end of each level you are awarded a number of medals if you have met the requirements which are coloured either bronze, silver or gold based on the difficulty level attached to the award. These can be viewed in the badges folder inside the archives on the games main menu.
There are a total of 8 artifacts that are collected as the player completes the story mode. After each case the player is awarded one item for successfully finding the culprit. These can be viewed from the archive in the main menu.
There are a total of 8 cases in the story mode which can be played in single player or co-operatively, but the outcome is the same each time as this mode is narrative driven and the crime is committed by the same person each time.
- Prologue - The Commodore's pudding has been stolen, and he has asked you to find the culprit.
- Dickens Manor - The Commodore's wife Olivia Dickens has been kidnapped and you must search the manor to find the culprit.
- Train - The conductor on the train has been knocked out and you must search the cabins in the train to find the culprit.
- Aquarium - Hugh the Manatee has been kidnapped from his tank and you must search the aquarium to find the culprit.
- Ship - The cruise ships wheel and anchor have been stolen, and you must search the ship to find the culprit.
- Opera House - A piano has been dropped on the theatre's flautist, and you must search the opera house for the culprit.
- Zeppelin - You must stop Mr Valentine from releasing his evil gas by searching the Zeppelin for the culprit.
- The Finale - Having rescued Olivia you must investigate the Dickens Manor to discover Mr Valentine's true identity.
There are many suspects that are present throughout the different cases in the game who also appear in multiple cases. They can be interrogated for clues or accused of the crime.
- Nurse - Dolly Bianca
- Columnist - Vendetta Clamp
- Judge - Judith Prudence
- Chef - Madeline Ash
- Starlet - Carlotta Johannesburg
- Maid - Fifi Fromage
- Singer - Griselda Wurstkrieg
- Teacher - Minnie Wigwam
- Poet - Ian Neon
- Doctor - Morgan Harvest
- Professor - Wilhelm Goiter
- Director - Lester Noogie
- Gardener - Schmoot
- Butler - Thaddeus Bilge
- Rocker - Rikki Krikket
- General - Ed Mission
Mr Valentine is the alias of the criminal mastermind and arch nemesis of The Commodore. While he is the suspect in the kidnapping of Olivia Dickens he is not a suspect that appears for interaction in the cases but instead appears throughout each case placing traps around the crime scene and triggers mini-games occasionally. Each of the culprits in the story mode's cases have been given a golden item in exchange for carrying out a task that plays in Mr Valentine's master plan. Mr Valentine often leaves behind a calling card in the form of a valentine card that contains a rhyming poem revealing his next location which leads the Dickens Detective Agency further towards him and in to another case.
The final case of the game involves interrogating suspects and investigating the Dickens Manor to find out the true identity of Mr Valentine.