The majority of the show's story has not changed from production to production, but many of the songs have been altered, cut or replaced since the show debuted.
Act I
The audience is introduced to John Utterson and Sir Danvers Carew, both having been associated with Doctor Henry Jekyll. Utterson was Jekyll's lawyer and best friend while Sir Danvers was Jekyll's future father-in-law. The two gentlemen take the audience back some time to find Jekyll in an insane asylum singing of his comatose father ("Lost in the Darkness"). It is Jekyll's belief that the evil in his father's soul has caused his illness. Jekyll tells the audience about his passion to find out why man is both good and evil and his attempts to separate the good from the evil ("I Need to Know").
Some time later, the rich and poor of 19th century London describe how people act – how they want others to see them, no matter who they really are inside ("Façade"). Afterward, Jekyll presents a research proposal to the Board of Governors of St. Jude's Hospital. Sir Danvers, the chairman of the board, is in attendance along with His Grace Rupert the 14th Bishop of Basingstoke, the Right Honorable Sir Archibald "Archie" Proops, Lord Theodore "Teddy" Savage, Lady Elizabeth "Bessie" Beaconsfield, General Lord Glossop and Simon Stride, the secretary. All, with the exception of Sir Danvers and Stride, are pompous, rich semi-hypocrites. When Jekyll proposes to test his theory and his formula on a human subject (presumably his father), they reject the proposal with cries of "sacrilege, lunacy, blasphemy, heresy", voting five to none with Sir Danvers' one abstention ("Board of Governors"). Utterson tries to calm Jekyll down, knowing that he is obsessed over his father's condition. Jekyll feels that he could "save" those who have fallen in the same darkness. Utterson urges his friend, if he feels he is right about his theory, that he should continue ("Pursue the Truth").
Later that night, a group of high society Londoners turns up at Sir Danvers' residence at Regent's Park, which has a well-maintained façade. Sir Danvers throws a showy party for his daughter Emma, for her engagement to Dr. Jekyll, to which Jekyll is late. ("Façade" (reprise #1). During the party, the guests – which include the Governors and Stride – mention how worried they are about Emma being engaged to a "madman", but both Sir Danvers and Emma back up Jekyll. Stride, who has feelings for Emma, speaks to Emma in private and tries to reason her out of her engagement, but she quickly turns him down, saying she feels she can be who she wants to be with Jekyll ("Emma's Reasons").
Jekyll arrives late as usual – just before the party leaves to go see the fireworks – and shares a moment with Emma. Though he warns her he may always be busy with his work, Emma swears she will be beside him through it all ("I Must Go On/Take Me as I Am"). Sir Danvers returns as Jekyll leaves and expresses to Emma that he considers Jekyll like a son to him but finds it difficult to tolerate his behavior at the cost of losing his daughter. Emma assures him that he will never lose her, and they should not be afraid to let go ("Letting Go").
Jekyll and Utterson later go to the dregs of Camden Town known as "The Red Rat" for Jekyll's bachelor party ("Façade (reprise #2)"). Prostitute Lucy Harris arrives late and is in for some trouble with the boss, known as 'Spider', but she dismisses it for now. Despite her position in life, she is seen to be kind-hearted and well-liked by her co-workers but has moments of contemplation about her life ("No One Knows Who I Am").
Guinevere, the German manager of "The Red Rat", then breaks Lucy's reverie and then sends her out onstage to do her number ("Bring on the Men"), which captivates Jekyll. After the number, Lucy begins to circulate among the clientele. Spider approaches Lucy and after striking her hard across the face, threatens to kill her if she is late again. Jekyll approaches Lucy after witnessing the Spider's actions and intends to help her as Utterson is led away by another bar girl. Jekyll and Lucy are drawn to each other in a way that promises each of them a great friendship. Jekyll admits Lucy's song has helped him find the answer to his experiment. Utterson reemerges, and Jekyll tells Lucy that he must be on his way. Before he goes, he gives Lucy his visiting card and asks her to see him should she ever need a friend ("Lucy meets Jekyll").
As Utterson and Jekyll arrive at the latter's residence, Utterson notices that Jekyll is in a better mood. Jekyll informs him that he has found a subject for his experiments. Utterson recommends that Jekyll go straight to bed and departs. Jekyll dismisses his butler, Poole, for the night and proceeds to his laboratory, excited that the moment has come to conduct his experiment ("This Is the Moment"). Keeping tabs on the experiment in his journal, Jekyll mixes his chemicals to create his formula, HJ7, and injects it into the subject: himself (in some versions, he drinks the formula, as he did in the book). After a minute of the potion's side effects, he writhes in pain, and is taken over by an alternate, aggressive personality ("First Transformation"). With grim humor he notes in his journal "4:00 AM -A few slight changes" (the exact line varies, depending on the production). He gleefully goes out and roams the streets, taking in the sights and sounds of London while tormenting innocent bystanders, which includes a sexually abusive encounter with Lucy (“Lucy meets Hyde”). Jekyll's alternate personality gives himself a name: Edward Hyde ("Alive").
A week later, no one has heard anything from Jekyll. Emma, Sir Danvers and Utterson ask Poole where he is, but Emma decides to leave and believes Jekyll will come for her after his work is finished. After Emma and Sir Danvers leave, Poole tells Utterson that Jekyll has been locked in his lab all this time and that he has heard strange sounds from the lab. Jekyll, who seems distraught, emerges and impatiently sends Poole to fetch some chemicals for him. Utterson confronts Jekyll about his bizarre behavior, but Jekyll brushes this off. He instead gives Utterson three letters: one for Emma, another for her father, and one for Utterson himself should Jekyll become ill or disappear. Suspicious and concerned, Utterson warns Jekyll to not let his work take over his life. Meanwhile, Emma and Sir Danvers argue about the prudence of Emma's marriage to a man who seems to be falling into an ever-deepening abyss. Emma again tells her father that she understands that Jekyll's work is important ("His Work and Nothing More").
After Utterson departs, Lucy arrives at Jekyll's residence with an aggressive bruise on her back. As Jekyll treats her wound, she tells him a man named Hyde inflicted it. Jekyll is stunned by this revelation but hides it. Feeling compassion for Jekyll for being kind to her, Lucy kisses him ("Sympathy, Tenderness"). Disturbed by his own actions, Jekyll leaves Lucy, who wonders about her love for him ("Someone Like You").
Later, the Bishop of Basingstoke is seen with Guinevere after having a "meeting" with one of her underage attendants. He pays Guinevere and arranges to see the attendant next Wednesday. When Guinevere and the attendant leave, Hyde appears holding a swordstick with a heavy pewter knob. After insulting the Bishop, Hyde proceeds to beat and stab him to death with the swordstick before gleefully setting the body aflame ("Alive (reprise)").
Act II
Utterson and Sir Danvers speak to the audience once again of past events with Jekyll: Utterson begins to feel he was not able to help his poor client and friend, while Danvers senses that something was horribly wrong with his work, as he had not been seen or heard from for weeks.
The citizens of London gossip about the bishop's murder as Hyde hunts down and kills General Glossop, Sir Proops, Lady Beaconsfield, and Lord Savage. By now, all five Governors who rejected Jekyll's proposal are dead ("Murder, Murder"). Later one night, Emma lets herself into Jekyll's laboratory. She finds his journal open and reads one of his entries. Jekyll enters and immediately closes the journal, preventing her from learning what he has become. Emma can see he is distraught. She professes her love for him and begs him to confide in her ("Once Upon a Dream"). He tells her nothing of his work, but says he still loves her. After Emma leaves, Jekyll writes in his journal that Hyde has taken a heavy toll on him and those around him, and that the transformations are occurring of their own accord. His entry is interrupted when Utterson arrives at the lab, seeking to find out who Jekyll's sole heir is, Edward Hyde, as referred to in Jekyll's letter. Jekyll only tells him that Hyde is a "colleague" involved in the experiment. Utterson can see that his friend is desperately ill and agrees to obtain the rest of the chemicals Jekyll requires. Jekyll, once again alone, begins to face the fact that Hyde is a part of him ("Obsession"). At the same time, both Lucy and Emma wonder about their love for the same man ("In His Eyes").
At "The Red Rat", Nellie and Lucy consider their profession and why they keep doing it ("Girls of the Night"). Lucy is then visited by Hyde, who tells her that he is going away for a while. He then warns her to never leave him. Lucy is terrified, but seems to be held under a sexual, animalistic control by Hyde ("Dangerous Game"). As they leave together, Spider addresses the "Red Rat" attendants, warning them to always be aware of what dangers lie ahead in the East End ("Façade (reprise #3)").
Utterson comes to Jekyll's lab with the rest of the chemicals and a secret envelope and discovers Hyde, who informs him that the doctor is "not available" tonight. Utterson refuses to leave the package with anyone but his friend and demands to know where he is. Hyde replies that even if he told him, Utterson would not believe him. Utterson insists on seeing Jekyll, threatening to alert the police otherwise. Hyde angrily attempts to attack Utterson who threatens him with his swordstick. Trapped, Hyde injects the formula into himself, roaring with laughter as he reverts to Jekyll in front of an appalled Utterson. Jekyll tells Utterson that Hyde must be destroyed, whatever the cost. He then begs Utterson to deliver money for Lucy so she can escape to safety. As Utterson leaves, Jekyll mixes in chemicals and injects the new formula, fearing that he might lose himself forever, and praying that he can restore his former life ("No One Must Ever Know").
Utterson visits Lucy at "The Red Rat" with the money, along with a letter from Jekyll that entreats her to leave town and start a new life elsewhere. After Utterson leaves, Lucy wonders of the possibilities ahead ("A New Life"). Just then, Hyde returns. Seeing the letter from Jekyll, he tells Lucy that he and the doctor are "very close" and that they "share everything". In some versions Hyde reveals that he feels that Lucy has betrayed him by being in love with Jekyll and by going to see him every day. He then calls Lucy over to him and holds her very close. As he holds Lucy softly so that she does not suspect it, he slowly, angrily and savagely stabs her multiple times before slitting her throat ("Sympathy, Tenderness (reprise)"). The vile murderer runs off laughing, just as the "Red Rat" attendants find Lucy's body and carry her out on a stretcher. Covered in Lucy's blood, Jekyll returns to his laboratory and faces off with Hyde in a final battle for control ("Confrontation").
Later, Utterson tells the audience that Jekyll had given up his task of "finding the truth", condemning his father to the darkness. Yet, as Sir Danvers would put it, the doctor had returned at "the sound of wedding bells" ("Façade (reprise #4)"). Several weeks later, Jekyll seems to have regained control as he and Emma stand before the priest at their wedding in St. Anne's Church. As the Minister begins the ceremony, Jekyll doubles over in pain and transforms into Hyde. Hyde then kills Simon Stride, a guest at the wedding, before taking Emma hostage. At the sound of Emma's pleading voice, Jekyll is able to regain momentary control. He begs Utterson to kill him, but Utterson cannot bring himself to harm his friend. Desperate, Jekyll impales himself on Utterson's swordstick. Emma weeps softly as Jekyll dies, finally free of Hyde's evil control ("Finale").
