Ransom Drysdale

Hugh Ransom Drysdale is Richard and Linda's son, referred to as the Black Sheep of the family. His sly tactics lead to him almost avoiding capture for his crimes, although he inadvertently kills Fran and is arrested.

Biography
The eldest grandchild of Harlan Thrombey and the only child of Richard and Linda Drysdale, Ransom grew up to be the black sheep of the Thrombey family.

Plot to Kill Harlan
The night of Harlan's 85th birthday, Ransom and Harlan got into a heated argument in his study. The fight reached a climax when Harlan revealed that Ransom, along with the rest of the family, had been written out of his will in favor of his nurse, Marta Cabrera. After angrily and futilely protesting, Ransom stormed off.

However, as he was driving away, a twisted plan took shape in his mind: if Marta were to be found responsible in any way for Harlan's death, the Slayer rule would take effect, nullifying Harlan's changed will and granting Ransom his share of the inheritance. To enact this plan, Ransom snuck back to the mansion, avoiding being seen by the video security and the rest of the family, reaching Harlan's study on the upper floor via a hidden door. There he found Marta's bag, which contained the medicines Harlan would be injected with later that evening (morphine and keterolac). Ransom used Marta's syringes to switch the liquids in the medicine bottles, believing that the Marta would accidentally give Harlan a fatal overdose of morphine: as a final precaution, he took Marta's bottle of nalaxone to prevent her from treating the overdose.

As he climbed back down the trellis, Ransom was spotted by Nana, although she did not alert the family.

First Hitch in the Plan
Ransom learned of Harlan's death in the paper the next morning: much to his surprise, however, the cause of death was a suicide rather than a medical error. Still needing to implicate Marta in Harlan's death, Ransom anonymously hired private detective Benoit Blanc to investigate the death.

Failure and Arrest
After Blanc shared his deduction with Marta, Ransom and the police, Marta received an update from the hospital on Fran's condition. Once Marta claimed Fran would survive, Ransom decided to confront Marta. He accused her of exploiting his family's kindness and trying to rob them of their birthright. Upon being ridiculed by Blanc over calling Harlan's mansion his "ancestral family home", Ransom lost his composure: admitting to "killing" Fran, Ransom ranted that the charges he could be convicted for (arson, attempted murder, etc.) would not garner him a long sentence, and he swore to wreak havoc upon Marta's life as soon as he got out. However, as he finished his threat, Marta vomited in his face Fran was, in fact, dead: Marta had lied long enough to trick Ransom into confessing to her murder, and Trooper Wagner had discretely recorded the entire confession on his phone.

Now facing life in prison, Ransom grabbed a knife from Harlan's collection and attempted to stab Marta in a last-ditch effort to ruin the woman who foiled his plans. However, the knife turned out to a harmless, retractable stage knife, leaving Marta rattled but unharmed. Ransom was swiftly restrained by the police and arrested for his crimes.

Trivia

 * The movie makes no secret that Ransom had something to do with the death of his grandfather. What is clever about the movie's mystery is that it's revealed that Ransom only made a small contribution to the death of his grandfather. Harlan actually did commit actual suicide but there was still a real murder mystery going...not Harlan's but Fran.