On the streets of Devil’s Acre, London, a growling beast is stalking a prostitute. The woman notices someone following her and playfully asks the stranger to come out of the shadows. Inspector Quick arrives and greets her. Suddenly the creature pounces out of the darkness and decapitates the prostitute in front of a rather mildly perturbed Quick. Elsewhere during the attack, sinister cultists are chanting demonic verses…
At the New Regency Theatre, Jago is wrapping up another evening show before retiring to his office. He is suddenly confronted by a young man jumping out of his wardrobe. Immediately assuming the man to be a thief, Jago subdues the man, who does not attempt to put up a fight. The man demands to see Henry Gordon Jago. Jago confirms his identity and is rather taken aback by the next word from the stranger…’Father?’.
At the Red Tavern, Quick fills in Litefoot and Ellie on his encounter with the horrifying beast. He describes it as a large hairy hybrid of a wolf and a pig. But most pressingly is that it is still on the loose. At the same time, people have been disappearing. Quick cannot help but think that the two are probably connected in some way. At that moment, Litefoot’s old friend, archaeologist Jean Bazemore, arrives at the Red Tavern and greets the Professor.
Meanwhile, Jago’s intruder introduces himself as Henry Gordon Jago Jr. (or Harry for short) and that he is the son of Jago. His mother, Ruby Valentine, told him that Jago had died recapturing an escaped elephant, but HGJ Jr. had a feeling she was lying. Jago cannot recall meeting a woman by that name and asks to know where she could be now. HGJ Jr. tells him that she has been kidnapped, hence why he sought out his father for his help.
Litefoot and Bazemore begin to catch up on old times, and Ellie immediately begins to admire the self-made woman. Bazemore explains that she is visiting from Egypt to protest the construction of a railway line across an archaeological site in London by the Metropolitan Railway Company.
Jago and HGJ Jr. travel to Devil’s Acre, as this was where HGJ Jr’s mother was taken. HGJ Jr. explains that he and his mother have been pursued across Europe by a sinister group who seemingly have spies everywhere, even in government…
Later, Litefoot and Bazemore are still recounting memories as they leave the Red Tavern. Suddenly, Litefoot hears a low, growling sound in the darkness. He orders Bazemore to stay near the Tavern as he investigates, but nonetheless she follows, much to Litefoot’s chagrin. They find nothing but a horrible scent, which Bazemore assumes is from the lion house at Regent’s Park.
At Devil’s Acre, Jago and HGJ Jr. disembark from their carriage outside an abandoned warehouse that HGJ Jr. claims to once belong to the Metropolitan Railway Company. He claims this is where the kidnappers brought his mother. They enter the warehouse and HGJ Jr. opens a trapdoor in the floor that leads below the warehouse. They walk through a tunnel that eventually leads to a dimly lit area that looks like a demonic chapel decorated in wolf skulls. They discover a dead woman on a sacrificial altar in the centre of the room…which HGJ Jr. solemnly identifies as his mother…
The next morning, Litefoot arrives at his mortuary and discovers Jago and HGJ Jr. asleep on his slabs, as well as HGJ Jr’s mother’s corpse on another slab. Litefoot awakens the two with a start and demands to know the situation. Jago takes Litefoot into another room to explain the situation and asks that he be discreet. Jago admits to his friend that he has no idea who his son truly is or who the woman is as he is never met her before...or remembered doing anything particularly regretful so to speak…
At the chapel, the leading cultist is reprimanding his disciples for abandoning their posts and allowing their ‘holy vessel’ to be stolen. He demands they retrieve the corpse and return it for the summoning ceremony…
At Litefoot’s house, Litefoot explains to Jago that the woman’s body did not suffer any sort of violence but died of a disease that he could not identify. He assumes that the disease is of alien origin and estimates that it has been festering inside her for the past 20 years. Litefoot produces a medallion that he found on the woman’s corpse and has a feeling that he is seen this before. Suddenly, they hear violence upstairs and a window smashing. The Infernal Investigators rush upstairs to where HGJ Jr. was sleeping. They burst into the room and are just in time to see a gang of hooded thugs wearing masks ride away with HGJ Jr. in captivity.
Bazemore is arguing with the head of the Metropolitan Railway Company. An explosion had recently dealt significant damage to the archaeological site and she believes that the company had a hand in the conspiracy. The head of the Railway Company is dismissive of her claims and promptly sees her off. Bazemore warns him that this will not be the last he hears from her. Once Bazemore leaves, the head sinisterly whispers that this is the last time…
Bazemore leaves the offices in a huff. She hears footsteps from behind her and is suddenly accosted by several thugs, but she promptly beats them all down.
Jago is anxious to chase after the masked hoods and rescue his son, but Litefoot dissuades him from doing so as they do not know what they are truly up against. Litefoot is more intrigued by the medallion and assumes that identifying it will help them track down their enemy. Unbeknownst to Litefoot, Jago slips out of the house. Moments later after sifting through several books, Litefoot identifies the medallion’s origin to…the Hellfire Club!
At the chapel, the Hellfire cultists deliver HGJ Jr. to the lead cultist. HGJ Jr. threatens them by stating that his father will find him and kill them all. The lead cultist tells HGJ Jr. that Jago is not his real father, and that HGJ Jr. will lead them to his true father’s kingdom of darkness!
Litefoot meets up with Bazemore at her archaeological site. Bazemore is sceptical about the Hellfire Club as they have seemingly disbanded over a century ago. But Litefoot assumes it is a group that have adopted the name. Bazemore mentions her accosting by a gang of thugs but did not bother to report them as they were hooded and wearing masks. Litefoot deduces that her thugs were a part of the same group that kidnapped HGJ Jr. from Litefoot’s house. Litefoot also explains that Jago had gone after the group alone after he left his friend a note and that he has informed Quick of his intentions, despite Litefoot’s warnings. He shows Bazemore the medallion, which coincidently shows up in a book that Bazemore had gifted Litefoot the night before. Bazemore becomes horrified and tells Litefoot to follow her immediately. She leads Litefoot to an excavated chamber and shows him the floor is decorated with the same symbol as the medallion…
Jago is in the tunnel making his way to the underground chapel. He reaches the end and witnesses the cultists conducting their demonic ritual. Mustering up courage, he bursts through the door to the chapel and announces himself to the cultists. The cultists swiftly subdue Jago and the lead cultist orders his disciples to execute him…until a familiar voice orders them overwise…HGJ Jr. fully dressed in high priest apparel. HGJ Jr. instead states that Jago is to be sacrificed at the climax of the ceremony when the Prince of Darkness will rise once more. The cultists stash Jago into another room…with a rather grotesque creature…
Litefoot is perplexed as to how the medallion’s symbol could be on the floor of an ancient chamber. Bazemore informs him the chamber is at least 200 years old, which predates the original Hellfire Club set up in the 18th Century. Litefoot discovers a slot in the chamber with the exact same symbols as the medallion, which he believes means that the medallion is actually a key. Litefoot slots the key into the hole and the chamber floor begins to open up beneath them and the two fall through the ground…
Litefoot and Bazemore discover themselves in an underground labyrinth. They are quick to reunite with Jago, who has been wandering around while dodging the beasts that lurk within. They look up and discover the ceiling above them has sealed up again, which means that they are trapped underground with the Hellfire Club. Bazemore leaves the room to confront the mad Satanists with Jago and Litefoot in tow.
The trio wander into the next room and discover it full of creatures in cages. They notice several cages have been destroyed, but not by humans or creatures, but an explosion. Bazemore deduces that the unnatural tunnelway in the room leads to the dynamite store of the Metropolitan Railway Company. Bazemore confesses that she had actually set the explosives herself to sabotage the railway company and pin the damage done to her dig on the company to keep them out of her way. But instead she inadvertently released one of the creatures from the cages and onto London! Jago surmises that they can surprise the cultists by appearing in one entryway while Quick and his men can cut off the entrance via the warehouse. Bazemore heads up the tunnel towards the dynamite store to rectify her mistake.
Above ground, Quick and his officers are evacuating the area when Bazemore arrives. Quick informs her that the escaped creature has been captured by the police in an abandoned house. She tells him to clear the area as she shows him some dynamite. She instructs him to place the dynamite at key positions to blow up the house and kill the creature.
Below ground, Litefoot discovers several pictures that depict horrible creatures. He deduces that these creatures in the cages are genetically deformed versions of existing creatures, noting one that looks like a wolf, a goat and an elephant. They notice an empty cage that has a picture of a human above it. They piece together why HGJ Jr’s mother was pursued across the world…she was an escaped lab rat from the Hellfire Club.
Above ground, Bazemore detonates the dynamite and obliterates the house with the creature inside. Before Bazemore can lead Quick into the tunnels to rescue the Infernal Investigators…they feel the ground shake beneath them…
In the chapel, the cultists are still chanting away despite the destruction unfolding around them. Jago and Litefoot arrive and discover HGJ Jr. tied to the sacrificial altar. HGJ Jr. is terrified claiming the cultists are entranced. Suddenly, a bolt of lightning strikes the altar. The altar begins to open revealing it to be a sarcophagus! A hideously deformed creature emerges from the sarcophagus. It immediately possesses the lead cultist and demands to know where it’s offspring are. It identifies HGJ Jr. as it’s son and the product of the genetic experiments that resulted in the monsters in the cages. Jago steps forward to defend his son, but the creature angrily strikes down Jago with a bolt of lightning. With the final moments Jago seems to have left, HGJ Jr. shows him a playbill that his mother carried around, it shows Jago standing in for a host at a theatre, thus showing how HGJ Jr. got his name. Jago fears that he about to die from his wounds. HGJ Jr. sings the song his mother used to sing as Jago begins to pass away as Litefoot tearfully listens. With his new resolve, HGJ Jr. promises to avenge him and angrily stands up to the demonic entity claiming to be his true father. The creature tries to coerce HGJ Jr. to join him and they can conquer the universe. Bazemore arrives with several officers. She is shocked to discover the lead cultist is the head of the Railway Company, but is more horrified by the demonic entity in the room, which can only mean the original Hellfire Club did dabble with a satanic monster. One terrified officer opens fire on the lead cultist…to no effect. The demon laughs and disintegrates the officer. With all the death taking its toll on him, HGJ Jr. takes the gun and shoots the demon dead, ending his father once and for all. It’s death triggers another explosion that blocks both exits from the chapel. Thankfully, Bazemore still has a few sticks of dynamite to spare. The explosion awakens Jago from his near death state, much to everyone’s delight. The group are shocked to discover that all the cultists and HGJ Jr. have disappeared in the chaos. More pressingly is why didn’t Inspector Quick join Bazemore and his officers on this raid?
Elsewhere, a hypnotised Quick meets with The Master. The Master is pleased that Quick followed his instructions and that everything is going according to plan…
At the railway station, Jago and Litefoot are preparing to say goodbye to Bazemore. The two men resolve to try and find HGJ Jr. With Bazemore awaiting Litefoot, Jago wisely makes himself scarce. Bazemore explains that the recent events have ruined all future plans for a her work on the dig, so she plans to return to Egypt to continue her other excavations there. Litefoot remarks how the Queen herself declared the order for the chapel and the catacombs to be sealed off, which is rather peculiar. Bazemore boards the train and reminds Litefoot to look her up should he be in Egypt.
