Marla Ridgely Moore

Marla Ridgely Moore was one of two murder victims from "Pick Your Poison," episode 5.10 of Elementary, only to be revealed as the episode's main villainess.

History
Marla was the daughter of wealthy furniture store owner Sam Ridgely, and the heiress to the Ridgely empire. She was also the ex-wife of Patrick Moore and the mother of their only son, Ethan, who was stricken with an autoimmune disease. However, the episode's progression revealed that Ethan had no signs of having an actual disease, and his "illness" was revealed to have been intentionally caused by Marla.

Several years prior to the events, Marla turned heel and stole her father's medications, and later used them to poison Ethan (a child at the time). The psychotic villainess committed the poisonings throughout Ethan's childhood and into his teenage years, doing so due to the attention she received from her son. As part of her twisted actions, the evil Marla constantly doctor-shopped to get more medications, which included visiting Krieg's office on two occasions--the second of which after phoning one of her aliases.

Marla gave inconsistencies that led to Krieg suspecting that something was off, with a main one being that she had given Krieg different ages for Ethan regarding the pinpoint of his illnesses, as well as mentioning juvenile arthritis when it wasn't listed as a symptom. Days before the events of the episode, Krieg revealed her suspicions to Ethan that Marla was poisoning him, while also revealing her own criminal acts as well. Enraged at his mother for stealing his life from him (as he spent his years as a shut-in due to the poisonings), Ethan returned to Krieg's office and shot both Krieg and Marla to death.

Personality
Underneath her wealth and status, Marla was a cruel and psychotic villainess; which was shown with her willingness to harm and nearly kill her child to gain the attention she craved. During Sherlock Holmes and Detective Marcus Bell's interview with ex-husband Patrick, Marla was referred to as a saint by Patrick, meaning that he had no knowledge of Marla's heel persona and her actions towards Ethan.

Motive
Other than wanting attention, no other distinct motive or factor was clearly revealed for Marla's evil actions. It was revealed that Patrick had a mistress, so it can be indicated that Patrick's cheating may have been a driving force for Marla to resort to villainous methods to get attention from Ethan.