This summary was deliberately written in the present tense (analysze it as if it’s taking place as you read it. )

As it happens, Steine loathes this book since it pictures a false, wicked image of Brighton riddled with crime.

As far as Steine is concerned, it is's been six years since the town iwas rid of villains.

If you're talking about an event that occurred in the past, you want to use past tense.

Before he can point that out to Jupiter, they’ve arrived in Middle Street, which is where the notorious “Middle Street Massacre” had unfolded six years ago.

"had" is ok to use, but it would be more natural to omit it.

All the while, it becomes more and more plain to Steine that Jupiter is gointg to use Brighton Rock’s references as insights into the logic behind Crystal’s murder.

Even though Harry Jupiter has never seet foot in Brighton before, such a prominent journalist like him should know better than to believe an old, fiction book in the first place.

And his being completely oblivious to the real Brighton is astounding and worse yet*.

I would just use "is even more astounding." You can add worse, but it would be a bit unnecessary.
It's hard to explain, but given the context of everything you wrote, people would understand that "worse" is a feeling he experienced.

No one can escape Jupiter’s charisma.

This is perhaps a matter of opinion: one would more often refer to "resisting" someone's charisma. "Escape" is a somewhat odd choice; if a native speaker wrote this, I would encourage them to use a different word, but one could conceivably choose to use it anyway.

So here they are now, walking the streets of Brighton in seekarch of valuable details for Jupiter’s piece on Crystal’s murder.

As it happens, Steine loathes this book since it depictures / presents a false, wicked image of Brighton riddled with crime.

The verb "to picture" is used more for in one's own imagination. The book depicts and the reader pictures it in their mind.

As far as Steine is concerned, it isknows, it has been six years since the town ishas gotten rid of its villains.

"As far as [someone] is concerned" presents it as a mere matter of opinion or taste; the next clause about how long it's been since the city has gotten rid of its villains is more of a factual matter. Concerning "has been" rather than "is"--I know you said you're intentionally using the present tense, but there's no avoiding the past tense here. FYI "villains" is a term mostly used in the context of the Marvel universe or else ironically or for comedic effect. If you're aiming for normal usage, "criminal" is more common.

All the while, it becomes more and more plain to Steine that Jupiter is gointg to use Brighton Rock’s references as insights into the logic behind Crystal’s murder.

Even though Harry Jupiter has never seet foot in Brighton before, such a prominent journalist like him should know better than to believe an old, fiction book novel in the first place.

"Fiction book" is not a common phrase. "Novel" is the most common. You could say "old work of fiction" but that's really only useful if you want it to be able to refer to other types of fiction including movies, plays, etc. Setting all that aside, if you were to say "old fiction book" you wouldn't use a comma, for reasons that confuse even native speakers. This article explains when to use commas between adjectives: https://prowritingaid.com/grammar/1008103/Should-I-use-a-comma-between-two-adjectives

*is it clear that I meant, “is even more astounding and worse”?

"even more astounding and worse" is better than "astounding and worse yet." However, even then, it's a confusing construction. I think you're just trying to emphasize how shocking it is, in which case you could try "is nothing short of astounding" (drop the "and worse").

This summary was deliberately written in the present tense (analyse it as if it’s taking place as you read it. ).

So here they are now, walking the streets of Brighton in seekpursuit of valuable details for Jupiter’s piece on Crystal’s murder.

Although Steine sort of agreed, he now rather regrets it.

The more they walk, the more it hangs over Steine that Jupiter isa massively into fan of the book “Brighton Rock”.

As it happens, Steine loathes this book since it picture a false, wicked image of Brightons Brighton, falsely, as a wicked place riddled with crime.

As far as Steine is concerned, it is's been six years since the town iwas rid of villains.

Before he can point that out to Jupiter, they’ve arrived inat Middle Street, which is where the notorious “Middle Street Massacre” had unfolded six years ago.

Knowing that Steine passionately caresis deeply interested about this pivotal event, Jupiter cunningly tries to look impressed by the place.

After a stiff and briebrief, stiff discussion about the surroundings, they carry on over to the seafront.

All the while, it becomes more and more plain to Steine that Jupiter is gointg to use Brighton Rock’s references as insights into the logic behind Crystal’s murder.

Even though Harry Jupiter has never seet foot in Brighton before, such a prominent journalist like him should know better than to believe an old, fiction book in the first place.

And his being completelyWhat's even worse is his astounding oblivious toness of the real Brighton is astounding and worse yet*.

*is it clear that I meant, “is even more astounding and worse”?

"Is even more astounding and worse" is really awkward phrasing, but the main point of the excerpt is clear.

As it happens, Steine loathes this book since it pictures a false, wicked image of Brighton riddled with crime.

As far as Steine is concerned, it ishas been six years since the town iwas rid of villains.

Before he can point that out to Jupiter, they’ve arrived in Middle Street, which is where the notorious “Middle Street Massacre” had unfolded six years ago.

*is it clear that I meant, “is even more astounding and worse”?

Yes :)