[Act Two]
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 that Jekyll will come for her when his work is finished. After she and her father depart, Poole tells Utterson that Jekyll has been locked in his lab around the clock and that he has heard strange sounds coming from the lab. A distraught Jekyll emerges and sends Poole on an errand, leaving Utterson alone to confront his friend about his behavior and warn him not to let his work take over his life. Meanwhile, Sir Danvers and Emma argue about Jekyll's behavior, with Emma vigorously defending her betrothed ["His Work and Nothing More"]. After her father leaves, however, Emma expresses her own private doubts and fears ["If You Only Knew"], while Jekyll gives Utterson 3 letters - one for Emma, one for Sir Danvers, and one for Utterson himself - and then writes in his journal about the toll that his experiment and the ever-increasing emergence of the Hyde personality is having on him ["Reflections (Jekyll's Soliloquy)"].
Lucy arrives at Jekyll's residence with a nasty bruise on her back, and asks to see him. As Jekyll treats her, she tells him that the injury was caused by a man named Hyde. Jekyll is disturbed by this, but hides his reaction. Feeling compassion for Jekyll for being kind to her, Lucy kisses him ["Sympathy, Tenderness"], but Jekyll, disturbed by his reaction, leaves her alone to marvel at their encounter and realize that she's fallen in love with him ["Someone Like You"].
As Jekyll wanders the streets, he suddenly transforms into Hyde. Coming across the Bishop of Basingstoke paying for sex from an underage Red Rat prostitute, Hyde beats and stabs the Bishop to death with a swordstick before gleefully setting the body aflame ["Alive [Reprise)"].
The citizens of London gossip about the Bishop's murder whilst Hyde goes on a murderous rampage, seeking out and killing General Glossop, Archie Proops, Bessie Beaconsfield, and Teddy Savage ["Murder! Murder!"].
Emma, concerned about Jekyll, sneaks into his laboratory and finds his journal open. As she starts to read one of the entries, Jekyll enters and closes it, preventing her from finding out what he has become. She professes her love for him and begs him to confide in her ["Once Upon a Dream"]. He professes that he still loves her, but doesn't tell her anything about his work. After she 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 ["Obsession [Streak of Madness)"]. Utterson arrives, seeking to find out who Edward Hyde - who is named in Jekyll's letter as being his sole heir - is. Jekyll tells him only that Hyde is a "colleague" involved in the experiment and asks Utterson to obtain some chemicals for him. Utterson, seeing that his friend is desperately ill, agrees, and leaves.
Meanwhile, both Emma and Lucy wonder about their love for the same man ["In His Eyes"].
The next day, Spider warns The Red Rat's employees about the dangers of the East End ["Facade (Reprise 3)"] and then confronts Lucy about an imagined slight, beating her. Backstage, she joins another prostitute, NELLIE, in lamenting the sad state of their lives ["The Girls of the Night"]. Hyde arrives and Lucy is at first terrified of him, but he begins to slowly seduce her and overcome her objections ["Dangerous Game"].
Utterson comes to Jekyll's lab with the remainder of the chemicals Jekyll asked him to retrieve and discovers Hyde, who informs him that the doctor is "not available" tonight. Utterson refuses to leave his package with anyone other than Jekyll and demands to know where he is. Hyde says that Utterson won't believe him if he told him and injects himself with the new batch of formula, transforming back into 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 his mind forever, and praying that he can restore his former life ["The Way Back"].
Utterson goes to see Lucy and gives her the money and a letter from Jekyll. After Utterson leaves, Lucy wonders at the possibilities ahead ["A New Life"], only to be surprised by Hyde, who tells her that he and Jekyll are "very close" and that they "share everything". Holding her slowly so that she will not suspect anything, he suddenly begins to stab her repeatedly and slits her throat ["Sympathy, Tenderness (Reprise)"] and then runs off as her body is found by The Red Rat's other employees.
Jekyll wakes up in his laboratory and is horrified to discover himself covered in Lucy's blood. He lapses into a waking nightmare ["The World Has Gone Insane"] that segues into a final battle for control with Hyde ["Confrontation"].
Weeks pass as Jekyll abandons his "quest for the truth" and he and Emma plan their wedding ["Facade (Reprise 4)"]. Moments before he and Emma walk down the aisle, however, Jekyll suddenly transforms back into Hyde and kills Simon Stride, the remaining member of the Board of Governors and a guest at the wedding, before taking Emma hostage. Utterson confronts him just as Jekyll momentarily regains control and demands that his friend kill him. When Utterson refuses, Jekyll desperately throws himself onto Utterson's swordstick ["The Wedding"]. Weeping softly, Emma cradles Jekyll in her arms as he dies, with the both of them lamenting the way that they lost the dream they'd planned on building ["Finale: Once Upon a Dream [Reprise)"].