SCENE 1: The show opens as two nameless garbage men (identified as Gruff and Toady in the script) haul a barrel with dangerous material, later identified as “atomic waste,” toward the shores of Phantom Lake. Gruff convinces his hesitant partner that what they are about to do is okay through an opening song which builds to a full-chorus number ending with the waste being dumped into the lake.
SCENE 2: Professor Jackson arrives at Phantom Lake from the local university to perform some science experiments with the assistance of his younger graduate assistant, Stephanie Yates. Stephanie is not-so-secretly smitten with the oblivious Professor. As they set up camp, she hints that she would like a romantic relationship with him. When she tries calling him by his first name, he rebuffs her advances with a Gilbert and Sullivan-style patter song (“Call Me Professor”).
SCENE 3: The five teen characters, two couples and their awkward fifth wheel friend are camping near Phantom Lake. Jonathan (the show-off) and Amy (the mean-girl) dance together as a couple near George (the boy scout) and Penny (the good-girl) around a campfire. Penny’s introverted and unpopular friend, Elizabeth, sits sullenly on a stump by herself. Penny insisted that she come camping with them to celebrate their recent high school graduation, but she is miserable. Amy and Jonathan taunt her incessantly, and George is only kind to her out of guilt from his girlfriend.
The teens stop dancing and Jonathan tells a scary story (song: “The Ballad of Lobo”) about a man named Michael Kaiser (nicknamed “Lobo”), who was a shell-shocked WWII soldier who supposedly went insane and murdered his wife. He later recovered, was devastated by guilt for what he had done, and disappeared into the woods near the lake to live as a hermit.
SCENE 4: We see that “Lobo” isn’t just a legend – he really does live in the woods nearby. He sees Gruff and Toady dumping something into the lake from a distance and decides to investigate. When he accidentally falls into the most contaminated part of the lake, he is transformed into a mutant algae monster filled with murderous intent.
SCENE 5: The Professor and Stephanie wake up at their campsite and spend the morning “Doing Science” (through a lighthearted waltz). They discover a frog with eight legs, coated in a mysterious black goo. Romantic feelings develop (and are unsuccessfully hidden by the Professor) as they work together. The pair are met at the lake-shore by “canoe cops,” Sven and Gustav (they patrol the lake via canoe). When the canoe cops leave, Stephanie discovers strange results returned by her laboratory tests on the goo.
SCENE 6: That morning, at the teens’ campsite, Penny and Amy are ready for a hike through the woods. They drag the boys and Elizabeth along with them. They discover the same black goo high up on a tree in the form of a strange-looking not-quite-human “hand print.” Elizabeth gets scared and refuses to forge ahead, so the others decide to leave her there by herself. Elizabeth wanders through the woods (singing “Afraid of Everything”), getting lost and hallucinating from fear along the way.
SCENE 7: Later that day, the Professor decides to serenade Stephanie with an original “rock-and-roll” song on his guitar, called “A Rockin’, A Rollin’, All the Way A Ramblin’” – it is not what most people would consider rock-and-roll. They are interrupted when Elizabeth and the other teens stumble into their campsite. After some discussion, the boys share that they found a strange hand-print made of the same black goo discovered by the Professor and Stephanie. Professor Jackson has the boys lead him to the print while the girls stay with Stephanie.
SCENE 8: The boys and Professor Jackson don’t find the print, but they do find an abandoned campsite, which turns out to belong to Michael Kaiser (“Lobo”). They know this when they find his dog tags, as well as a musical locket with a picture of Lobo’s wife (who bears a striking resemblance to Elizabeth). The locket also plays a musical theme which returns throughout the show.
SCENE 9: Back at the campsite, Stephanie and the girls talk about their futures. They give Elizabeth relationship advice: if she ever wants to find a guy who will like her, she’ll need to go to college (50s 12/8 ballad, “College”). When the Professor and boys return, Stephanie compares her findings with theirs. The black goo shows signs of being an algae/human hybrid. The boys scare Elizabeth with their discovery that Lobo is real and Elizabeth looks like his dead wife! The teens return to their campsite, and Professor Jackson admits to overhearing Stephanie talking to the girls about her feelings for him. He says that “perhaps someday” their relationship can be something more before going to his tent for the night. Stephanie sings “Someday.”
SCENE 10: The scene cross-fades to Gruff and Toady back at the lake one final time. As he approaches the water, Toady is pulled in by the Monster (formerly Lobo). As Gruff goes to see what happened, he is also pulled underwater. Act I ends as the Monster slowly emerges from the water to be fully revealed for the first time.
SCENE 1: Act II opens with the teens dancing around the campfire at night while listening to the radio. Canoe cops, Sven and Gustav, are floating on the lake in the distance, where they sing “Paddlin’ Along” and then discuss how something about the lake doesn’t seem right tonight. Without notice, Sven is pulled into the water by the Monster’s hand. Gustav is attacked soon after. The focus shifts to Elizabeth, who hears their screams in the distance. The other teens don’t believe her and continue dancing.
SCENE 2: Jonathan and Amy silently sneak off into the woods to make out. As things heat up (song: “Going All the Way”) and they reach the climax of the song, they are both attacked by the Monster.
SCENE 3: Jonathan and Amy’s screams are heard back at the campsite by the rest of the teens. They debate which action to take. George, Penny, and Elizabeth reluctantly decide to brave the eerie silence and dark woods to see if their friends need help.
SCENE 4: Elizabeth begins to panic as George and Penny lead her through the forest in the dark (reprise: “Afraid of Everything”), George attempts to calm her (and himself) down by getting the group to join in singing a jaunty tune. He says that “Nothing Bad Can Happen (When You Sing),” through a frantic vaudeville-esque song that ends, ironically, with both himself and Penny being attacked by the Monster. Elizabeth witnesses the terror firsthand and begins to fall apart. When she finally regains her composure (with nothing to lose) and faces the Monster and her impending doom, the Monster reacts in a surprising way. He stops, seeing in her face that of his former wife, as the tune from her locket plays in the underscore.
SCENE 5: Elizabeth retreats to the Professor’s campsite, where he and Stephanie try to calm her. They say that her friends were probably pulling a prank on her. The Monster then appears in their campsite and they all see it. Again, Elizabeth is caught between it and the scientists, and the Monster retreats peacefully. Professor Jackson is convinced that the black goo is causing shared hallucinations, but soon puts the pieces together and realizes that the Monster is actually the mutated Michael Kaiser / Lobo, and that he is reacting to Elizabeth because she looks like his wife.
SCENE 6: George stumbles into the Professor’s campsite and collapses, covered in mud and in tattered clothing. He sings that he survived the Monster’s attack (“Bones, I Tell You! Bones”) and wants to warn the others that the Monster is coming back for them. With the remaining characters in a panic, George dies in front of their eyes, clutching a human bone that he found that belonged to one of his friends.
SCENE 7: The Professor leads Stephanie and Elizabeth (the only survivors) to the place where the atomic waste was dumped into the lake, explaining his plan to stop the Monster by preventing it from returning to the water. He tells Elizabeth that she’ll have to be brave and stand between the Monster and the lake in order for the plan to work. In the danger of the moment, he finally tells Stephanie to call him by his first name, and they share a kiss. Before he is able to convince Elizabeth to do her part, the Monster emerges for a final hand-to-hand showdown.
The Professor and Stephanie try to fight the Monster but are quickly thrown aside as it makes its way toward the water. Elizabeth finally musters the courage to be brave and throws herself between the Monster and the lake. It is unable to fight her, and collapses to the ground as it dries out. The lake seems to once again be safe. A final warning about the dangers of pollution (“The Ballad of Lobo – Reprise”) is sung to the audience, Elizabeth’s courage is celebrated, and Michael Kaiser is memorialized not as a monster, but as a man.