The dossier
A caregiver at the centre of a very deliberate puzzle
Marta Cabrera works as the personal nurse for Harlan Thrombey and becomes entangled in the investigation of his death. She cannot lie without vomiting. The film makes that response both her greatest weakness and its central dramatic engine.
The Thrombey family is built around inherited wealth and the performance of respectability. Marta is the one person in the house whose behaviour is involuntarily honest. That honesty makes her readable to Detective Blanc and makes her dangerous to everyone with something to hide.
Ana de Armas plays Marta with a careful vulnerability that does not tip into passivity. She is scared and she makes mistakes, but she also makes decisions. The film's argument that goodness can be strategic rather than naive runs entirely through her performance.
Knives Out builds its whodunit around Marta rather than against her, which inverts the genre's usual structure. The audience is not trying to work out who she is. The film shares the truth early. It then watches a decent person navigate a world designed to destroy her.