Marta Cabrera

Marta Cabrera, played by Ana de Armas, is the main protagonist of Knives Out (2019). She lives with her mother and sister (Alice Cabrera) and works as Harlan Thrombey's registered nurse. Marta and Harlan are close friends, and he secretly makes her the sole inheritor of his estate. Marta's plight is complicated by a medical condition that causes her to vomit upon telling a lie. She ultimately exploits this by telling a lie and holding down the vomit just long enough for Ransom to implicate himself in Fran's murder.

Character
Marta has brown hair and brown eyes. Her age is unknown but its likely she is in her late 20s or early 30s. Her education is unknown, except that she has received her nursing license and is a registered nurse (RN). She at first seems like a timid character, but it is revealed that she is nervous about the investigation. Ana de Armas, the actress who plays Marta, characterizes Marta as having strength, self-control, and clear priorities. Her family is important to her.

Marta has a mother (unnamed) and a sister named Alice Cabrera. Marta's mother is undocumented. The dialogue throughout the film emphasizes tension about her family's ethnicity and immigration status.

Career
Marta is a registered nurse hired directly by Harlan Thrombey to work in his home, and she receives a flat fee. She is not part of a VNA (visiting nurse agency). She is characterized as being a good nurse by Benoit Blanc as she can tell the minute differences in viscosity between Harlan's medications.

Relationship with Harlan Thrombey
Harlan hired Marta directly to be his personal nurse. Harlan then payed her extra to stick around for more hours. Marta realized Harlan needed a friend and gladly took on that role. They developed a tight friendship and because Marta treated Harlan with genuine kindness, she is the one that he left his entire inheritance to, much to the chagrin of the Thrombey family.

Relationship with the Thrombey Family
Marta's relationship with the Thrombey family is complex. She seems to have a good friendship with Meg and tries to be tolerant with the rest of the family as anybody would but it does get complicated. She then decides its best to not financially support the family as its what Harlan would have wanted (not to mention most of them tried to threaten or blackmail her when she got Harlan's inheritance). If anyone, it is likely the only two people she might help are Meg and Nana.
 * Harlan Thrombey (best friend-employer)
 * Mrs. Cabrera (mother)
 * Alice Cabrera (sister)
 * Fran (close friend)
 * Meg Thrombey (close friend)
 * Benoit Blanc (partner-in-crime (temporary); later good friend)

Supposed Cause of Death
On the night of Harlan's death, he mimics an earthquake and knocks over a Go board to prevent losing the game to Marta, but he also knocks his medical supplies to the ground at the same time. He normally receives regular injections of ketorolac, an anti-inflammatory drug, and as needed doses of morphine, a strong pain reliever. She picks up the supplies and, without visually checking, administers what she believes is ketorolac through his port. She places the first bottle down and picks up the next bottle, but its label reads ketorolac. This leads her to think she mixed up the bottles and had accidentally administered a fatal dose of morphine to Harlan. Marta tells Harlan and immediately begins looking through her nursing back for naloxone, an opioid overdose reversal drug that comes standard with morphine prescriptions. She cannot find it and attempts to call an ambulance, but Harlan stops her because of the potential consequences to Marta's career and family. He creates a plan to make his death appear like suicide to cover up her mistake. This scene is a red herring.

Real Cause of Death
In the film's conclusion, Benoit Blanc reasons that Ransom Drysdale had used the syringes in Marta’s nursing bag to switch around Harlan’s bottled fluid medications, and removed the naloxone (anti-toxin) from the bag. By switching the medications, Ransom anticipated Marta would cause Harlan to overdose. His intent was to frame her for malpractice in order to nullify Harlan's last will, which disinherited the entire family and made Marta the sole inheritor. However, Ransom did not account for Marta's intuitive nursing skills. In the initial scene, it appears that Marta had incorrectly administered the medication and accidentally gave Harlan a fatal dose of morphine, as she did not check the bottle before administering the medication. But in the reveal scene, it is discovered that her apparent oversight actually causes her to correctly administer ketorolac even though it was in the morphine bottle - she can instinctively tell the difference between the medications by viscosity alone. This is confirmed in Harlan’s blood work: No morphine was found in his body. Harlan's refusal to listen to Marta and call an ambulance meant they never discovered the medication had been switched, and his suicide was truly a suicide.