As another reviewer says, this is Liz Wakefield's world, we're just visitors in it. Liz dominates most of the book, so let's get the two minor subplots out of the way:
(1) Portia Albert, one of the HIS peanut gallery, is struggling with the idea of inviting her famous actor father to see her in perform in her play, a part she attained with an alias. Eventually she does work up the guts to invite him to see her perform, and of course he loves it and immediately walks back all the horrid things he's ever said to her about being an actress. Happy ending!
(2) The rumors of the missing princess are getting out of control, up to and including 72-point headlines that she's been murdered. This is the final straw for a lot of people, including Eliana herself. David, her erstwhile Liverpool beau, discovers the truth about her by comparing her picture in the paper to the girl herself, and then declares that he doesn't care and loves her anyway, blah blah blah. They work out a whole big press conference to announce that he's "discovered" her and thus is eligible for the £1m reward, which he is going to use to set up a clinic for the London homeless and put himself through medical school, with full backing from the royal family. Happy ending!
(3) Elizabeth has fallen completely under the sway of Lord Byron manboy creep Luke and is convinced that the person who killed the doctor, nurse, and poodle in the previous novel - and Joy Singleton, the blond found in Jessica's bed at Pembroke Manor - is, in fact, a werewolf. She also suspects that the killer is Jessica's boyfriend Lord Robert Pembroke Jr, mostly because Luke convinces her that the only person who could've killed all of these people (and dog) is one of the Pembrokes. It's really obvious and really stupid how much sway Luke holds over Liz's "investigation," and of course she tells him everything because she is a smug asshole/blithering idiot.
Liz discovers that Lord Pembroke shares Luke's obsession with werewolves and werewolf hunting, but she considers Pembroke's obsession creepy while Luke's is somehow understandable? Yeah, okay. She also overhears Lord Pembroke considering the evidence that points in Robert Jr's direction, and that convinces her that Jessica is in mortal danger. She literally runs around London like a chicken with her head cut off, trying to find Jessica to warn her about Robert.
Jessica, meanwhile, is heartbroken that Robert has broken a date and left town (the country?) without telling her why, so she's maxing out her parents' emergency credit card at Herrod's on a retail therapy shopping spree. She's attacked in the subway, however, by something big and hairy and growling. When Liz hears this, she's more convinced than ever that Robert Jr is dangerous and the werewolf killer.
Liz and Jess have a big falling out at the beginning of the book when Liz accuses Robert of being the killer, based on her own irrational hatred of him. Jessica tells Liz that Robert is the first boy she's cared about since Sam's death and why can't Liz be happy for her? (JUSTICE FOR SAM!) Liz also references the Greatest Miniseries of All Time(TM) when she alludes to being on trial for manslaughter. Honestly, this was the high point of the novel.
The "evidence" against Robert is so obviously planted to frame him that it's hard to believe anyone takes it seriously. The police investigation that's described is more akin to a bad American farce than an English/Scotland Yard investigation, and the adults in the room - Lord Pembroke, Andrew Thatcher the "chief of police," Lucy Friday, Tony Frank, and others at the newspaper - act very blithely about the entire situation. Even as a teenager I would've been looking side eye at all of this because it makes not a damn bit of sense. If the ghostwriter has even touched a Golden Age detective novel, I'd be in shock. (The secret key to the "wolf lair" at Pembroke Manor is a copy of Dr Jekyll and Mr Hyde, which - WHAT??)
This book is downright awful. Beyond so-bad-its-good, this has circled back into how in the hell did this get published?? territory. Even by mid-90s YA standards, this is absolute dross. It's thrown together in such a terrible, slapdash way that even the tenuous link with reality is gone. It's very obvious that the ghosties didn't bother to do the bare minimum of research into, well, anything. It actively made me angry to plow through this <200 page book. If it wasn't for the nostalgia re-readathon, I would've quit after about 15 pages.