In a world where nothing seems to ever work out as you had hoped, The Rehearsal features Nathan Fielder helping ordinary people rehearse difficult conversations or life events through the use of sets and actors hired to recreate real situations. The situations can be trivial, like confessing to a lie about educational history, or more complex, like raising a child. Fielder commissions extravagant sets with every detail recreated. He hires actors to inhabit these sets and practice different dialogue trees with his clients dozens of times. Information used to train the actors and build the sets is often collected without the subjects' knowledge.
In the firs episode, Nathan Fielder helps Kor Skeete, a Brooklyn-based trivia aficionado who wants to confess to his bar trivia team that he lied about having a master's degree. Nathan reveals an elaborate method of rehearsals involving an actor (K. Todd Freeman) playing a 'fake Kor'. To help Kor rehearse the difficult conversation with his teammate Tricia to clean this long-held lie, Nathan creates simulations of trivia night with a fake Tricia in a full-scale replica of the Alligator Lounge, a Brooklyn bar. Kor overcomes his fears and makes his confession to the real Tricia.

Nathan stages a ninth birthday party for Adam, but faces a problem when Remy, one of the child actors who played Adam at age six, becomes attached to Nathan, calling him 'daddy' even after his scenes are over. Remy's mother explains that her son might have trouble understanding the difference between acting and reality. To discover what went wrong, Nathan repeats Remy's scenes with different actors including Liam (a nine-year-old Adam actor), an adult actor, and a mannequin. He then explores what might have happened if Angela had stayed with him and meets with the real Angela, who urges him to forgive himself, as her religious beliefs state.
In an attempt to truly understand the connection between parent and child, Nathan stages a new scenario in which he is Remy's mother Amber and Liam portrays Remy. They re-create the experience of appearing on The Rehearsal and becoming attached to 'pretend daddy' Nathan. After coming to the emotional realization that they should not have done the show, Nathan as Amber seemingly breaks character and tells the fake Remy, 'I'm your daddy.'

Episode three explores the mind of one of the most fanatical of all Nazis and the insight that gives into the psychology of dictatorship. Hess is brought to Nuremberg from the UK where he had flown 4 years earlier much to the bemusement of the British. Overy explains that they must have quickly realised he was not normal. In the intervening time Hess’s mental state has further deteriorated and when interviewed by Chief Interrogator Colonel John Amen proclaims amnesia. Chief Interpreter Richard Sonnenfeldt explains that they brought in Göring to confront Hess but that he too failed to make an impression.
Psychopathologist Prof. Edgar Jones proposes Hess’s behaviour patterns may be his way of escaping reality as he is forced to face the extent of the atrocities and choose between accepting his part of the blame or forsaking his Führer. However, as history Professor Robert Gellatel explains it is difficult to construct a case against Hess as he was imprisoned in England when the worst of the atrocities were carried out so British Prosecutor Mervyn Griffith-Jones must argue a conspiracy charge linking the pre-1939 persecutions to the post-1939 atrocities and a crimes against peace charge proving the flight to Scotland was merely a ruse.

In the second episode, Nathan develops a rehearsal for Angela, a woman considering motherhood. Nathan hires child actors to simulate adopting and caring for a baby and sets her up in a rented farmhouse in rural Oregon. Due to Oregon child protection laws, Nathan's team must covertly switch out the baby every four hours and replace it with a robot baby at night. Seeking a simulated husband, Angela dates Robbin, a numerology-obsessed man who wants to have sex with Angela despite her devout Christian beliefs against premarital sex. When Robbin quits the project due to the robot baby's incessant crying, Nathan inserts himself into the experiment as Angela's non-romantic co-parent.

What if you could combat aging and discover the full potential of the human body? Global movie star Chris Hemsworth, despite being in peak superhero-condition, is on a personal mission to learn how to stay young, healthy, strong, and resilient. Undergoing a series of epic trials and extraordinary challenges in order to understand the limits of the human body, he'll learn firsthand how we can live better for longer by discovering ways to regenerate damage, maximize strength, build resilience, supercharge memory and confront mortality.
Ever since his teenage years, stress has been part of Chris’s life, and he wants to learn how to deal with it better. Psychologist Modupe Akinola challenges him to stay calm during a terrifying walk along a crane that’s projecting out from the roof of a skyscraper. Modupe will train Chris in powerful physical and psychological techniques we can use to control the stress in our lives and combat the risk it poses to long-term health.

Dr Michael Mosley traces the sinister ways the experimental psychology has used to try to control our minds. He finds that the pursuit of mind control has led to some truly horrific experiments and left many casualties in its wake. Extraordinary archive captures what happened - scientists systematically change the behaviour of children; law abiding citizens give fatal electric shocks; a gay man has electrodes implanted in his head in an attempt to turn his sexuality. Michael takes a hallucinogenic drug as part of a controlled experiment to try to understand how its mind-bending properties can change the brain. This is a scientific journey goes to the very heart of what we hold most dear - our free will, and our ability to control our own destiny.