Now, for the part at the very end where Blanc runs through Ransom’s entire plot, which happens so fast that you might miss an intricate detail or two: Blanc has deduced that Ransom switched the labels the two medicines that Marta gives Harlan — one being morphine, which is lethal if given at the dose of the other medication — and that he also stole the antidote from her bag. But, Marta instinctually gave Harlan the correct dose of both medications, because rather than looking at the labels, she knows the weight and feel of each liquid, which means she grabbed the right medication despite the mix-up (one liquid is more viscous than the other). Unfortunately, she did look at the label after giving Harlan the medication, leading him to believe he was about to die, which leads him to commit suicide as part of the coverup to save Marta. (Blanc got this information after finding a toxicology report that Fran hid in the home and seeing that there wasn’t actually a high dose of morphine in Harlan’s system in a truly masterful scene earlier in the movie.)