In Glass Alibi, you either play as a Suspect in a crime or as the Detective trying to solve it. Each game starts with the Detective making up a crime and accusing the other players of committing it. No one knows who is guilty until the very end, and players have to make up excuses, relationships and alibis in order to not become the criminal.
The Detective asks the suspects questions so they can get to the bottom of who-done-it. Suspects have to think on their feet, while making sure they don't contradict their own narrative and attract the Detective's attention.
When Suspects draw the attention of the Detective by saying something strange or inconsistent, they can play cards from their hand as Alibis. These cards act as hard-evidence, solidifying their story and diminishing the Detective's suspicions.
Suspects can also use these cards offensively, accusing other Suspects of acting suspiciously, and turning the gaze of the Detective away from themselves. Just watch out you don't accidentally place yourself at the scene of the crime!
—description from the designer