Each sister is only allowed to leave their apartment on the day of the week that matches her name.

Monday did not disappear by accident. Desperate to protect her own unborn twins and live a life as a "real" person, she made a deal with the CAB's leader, Nicolette Cayman, to fund her campaign and eliminate her sisters. Ending and Themes 'What Happened to Monday?' Ending Explained - Collider

They must mirror each other's physical appearance exactly; for example, when one sister lost a fingertip in an accident, Terrence was forced to remove the same portion of the finger from all seven girls. Plot and Conflict

The story follows seven identical septuplet sisters—named Monday through Sunday—who are raised in secret by their grandfather, Terrence Settman. To remain undetected, they all assume the single identity of "Karen Settman" in public.

The status quo shatters when Monday fails to return home after work. As the remaining sisters investigate, they uncover a series of dark truths:

In the 2017 dystopian thriller , the world faces a catastrophic overpopulation crisis. To survive, the European Federation enforces a strict "One-Child Policy" managed by the Child Allocation Bureau (CAB), which claims to place additional siblings into cryosleep until the planet stabilizes. The Core Premise