The 20th and final season of Law & Order premiered on NBC on September 25, 2009, for which it was moved from its previous time slot to air on Fridays at 8 p.m. ET for the NBC broadcast. L&O was moved to Monday nights on March 1, 2010 with a two-hour telecast at 9 p.m. ET, before settling into its new time slot at 10 p.m. the following week, March 8.
During the season, The Jay Leno Show in primetime was cancelled and Leno returned to the 11:35 pm Tonight Show because of affiliate dissatisfaction. Three more episodes of Law & Order were ordered to fill the primetime gap, increasing the number of episodes for the season to 23.
In early January 2010, NBC initially announced they were going to renew Law & Order a 21st season. NBC's President of Primetime Entertainment at the time, Angela Bromstad, said, "I’m a "Law & Order" junkie... I wouldn’t want to be responsible for not having "Law & Order" break the record." But on May 14, 2010, NBC abruptly cancelled Law & Order after 20 seasons on the air, tying it with Gunsmoke as American network television's longest-running, regularly scheduled primetime drama. The final episode aired on NBC May 24, 2010.
The late announcement of the cancellation resulted in Law & Order not having a "series finale" episode. Had the series continued, it would have been the last to feature S. Epatha Merkerson, who prior to the cancellation announcement had herself announced that she would not return for the 21st season.
When a war veteran is found dead in a parking garage, all signs lead to a law professor whose past work as a lawyer for the Department of Justice unveils torture during wartime.
A crime scene investigator is found dead with her unfaithful fianc? as the prime suspect. However, when a young journalist is attacked and linked to the crime, this open-and-shut case may not be as simple as it originally seemed.
What seems like a kidnapping gone wrong turns into a terrorist investigation.
When a mother of ten adopted special needs children is found dead, the Detectives uncover an affair and a reality TV show offer.
A late-term abortion doctor is murdered and a pro-life protestor is investigated.
The Detectives investigate a website with threatening web posts.
A rich young woman is murdered, linking her to a drug cartel.
A deadly car crash reveals a pharmaceutical whistle-blowing plan gone horribly wrong.
A case that begins as a search for a missing witness spirals into a murder conspiracy with ADA Connie Rubirosa (Alana De La Garza) caught right in the middle.
A man defends his store from an armed robbery that may have been a scare tactic for a shakedown.
During an election, a campaign volunteer is found dead with the word "FED" written on his chest.
A freelance journalist is murdered. The detectives find a connection between her and a talk show host who has had a series of workplace affairs.
A family of four is murdered in their home and both suspects have questionable mental states.
The detectives investigate the death of a high school student, which leads them to questioning the adults in his life.
A young woman's body is found in a hotel food-service cart, and the murder investigation turns up superficial evidence implicating a medical student who may be using a research project as a ruse to commit crimes.
Cutter takes on his mentor, Emily Ryan (Amy Madigan), when she tries to overturn the conviction of a man found guilty of a hate crime, and a secret from Cutter's past may affect the trial's outcome. Lisa Klein: Anna Chlumsky.
A man shoots four police officers to death, and the investigation reveals a protective mother and evidence that the victims may have known the shooter. When an arrest is made, the ensuing trial pits cops and detectives against the prosecutors.
A global-warming symposium becomes a crime scene after a scientist is poisoned and collapses during a speech. Detectives Lupo and Bernard initially suspect rivals from his field of study, but a messy custody battle points the investigation toward the victim's family.
A young model is found dead shortly after crashing an exclusive political event.
A young woman turns up dead in the back of a limousine and her death uncovers a clinic that provides family members of wealthy cancer patients an early payday.
A man is mysteriously left at a hospital with fatal stab wounds.
A crew from a reality television show discovers a dead man's body locked in a dog cage.
Olympic Gold Medalist Lindsey Vonn guest stars as detectives investigate a potential school attack after video footage of explosives surface on an Internet blog site. When Lieutenant Anita Van Buren (S. Epatha Merkerson) discovers a blog site featuring video of an alarming amount of explosives, Detective Cyrus Lupo (Jeremy Sisto) and Detective Kevin Bernard (Anthony Anderson) race against time to find the anonymous blogger before plans to blow up a school are put into action. The Department of Education's refusal to take the threat seriously and resistance from the teachers' union further complicate the investigation. Fortunately, an administrative assistant at the teachers' union, Alicia (guest star Lindsey Vonn), gives the detectives a tip to lead them in the right direction. Meanwhile, Lieutenant Van Buren struggles to keep her personal issues from becoming public. Also Starring: Sam Waterston (D.A. Jack McCoy), Alana de la Garza (A.D.A. Connie Rubirosa) and Linus Roache (A.D.A. Michael Cutter).