Margaret "Maggie McFierce" McPherson is the first ex-wife of defense attorney Mickey Haller, the mother of Hayley Haller, and a prosecutor with the Los Angeles County District Attorney's Office in Van Nuys. She and Hayley live in a two-bedroom condo on Dickens Street in Sherman Oaks.
McPerson met Haller as they were going through the metal detector at the courthouse on her first day of work for the D.A. She was going to orientation and he was going to a courtroom for a case. She and Haller divorced after eight years of marriage due to their careers being opposite each other: Haller was defending criminals, while McPherson was attempting to prosecute them. They share joint custody of their daughter and they remain friendly. In many ways they act as though they are still married. They argue regularly, mostly about their daughter and they have sex occasionally, but they are careful not to criticize each other in front of their daughter.
Her career at the D.A.'s office has not been stellar. It appears that this is primarily due to sexism or internal politics rather than any failing on her part. As a result she was stuck in the Van Nuys office rather than the more prestigious downtown headquarters. Despite her lack of advancement, she takes every case seriously and believes in her mission as a prosecutor.
In early March of 2005 the case of Louis Roulet was assigned to McPerson to prosecute. When Roulet selected Haller as his defense attorney it created a conflict of interest, forcing the D.A.'s office to assign the case to another prosecutor. In an unguarded moment in a bar on St. Patrick's Day, she told Haller about a possible prosecution witness named Corliss who might have damaging testimony against Roulet. After that she had no direct involvement in the case until the conclusion when she worked with the police to set a trap for Roulet.
When Haller was appointed as a special prosecutor to overturn the exoneration of Jason Jessup, a convicted child-murderer who was freed after DNA evidence cleared him of wrongdoing, Maggie was named along with Mickey's half-brother, Detective Harry Bosch, to the team to prosecute Jessup. D.A. Gabriel Williams promised that Mc Pherson would be promoted to downtown if Jessup was convicted. There was initially some friction between Maggie and Haller, but things settled down and they worked well together. She handled the preparation and testimony of Sarah Landy (Gleason) and did very well. However, since Jessup was killed rather than convicted, McPherson did not get the promotion. On the positive side, this case created an opportunity for Hayley Haller and Madeline Bosch to get to know each other.
On 12 October 2011, Maggie was assigned the prosecution of serial killer Chilton Hardy, Jr. By this time she had been transferred from Van Nuys to the Major Crimes unit.