In the first pages of Donato Carrisi’s new thriller, The Hunter of the Dark, we are introduced to Marcus, an amnesiac who has woken up to discover he’s a priest, and not just your common or garden variety. “You will be able to say who you are only in the time that elapses between the lightning and the thunder,” he is told by his mentor, perhaps a little portentously. “The last representative of a holy order. A penitenziere [a priest who administers penance]... Once, though, people called you hunters of the dark.”

It’s a pleasingly dramatic opening for a novel that is happy to shade into melodrama. Marcus, who takes up his task willingly, is able to see “what others didn’t see. He saw evil. He detected it in the details, in the anomalies. Tiny tears in the fabric of normality. A low-frequency sound hidden in the chaos.” He’s put on the trail of the “Monster of Rome”, a serial killer who has been gruesomely knocking off couples around the Eternal City while easily eluding the police. Also on the case is forensic analyst Sandra Vega, a woman Marcus first met in Carrisi’s The Lost Girls of Rome – he is drawn to her, despite his vows of secrecy and celibacy, and she shares information from the police investigation with him.

Vatican City... where greatness has been ‘fed with blood’. Photograph: Jean Du Boisberranger/Hemis/Corbis

Carrisi’s fourth outing in English is a sometimes bewilderingly busy novel, with storylines barging in from all angles. Orgies, upside-down signs of the cross, a reformed neo-Nazi, a strange doll-like figure, a symbol of a man with a wolf’s head – they all play a part, as Marcus and Sandra begin to suspect that someone, somewhere, is protecting the monster.

“Evil is the rule. Good is the exception,” is the refrain that echoes through a novel that can run to clunky phrasing and odd dissonances, which could sometimes be the fault of the translator but isn’t always. “You’re pulling my leg,” an Italian policeman says, a little too laconically, when he’s faced with an unlikely cover story from villains with guns and a bound and gagged victim. Carrisi’s police force, meanwhile, appear bafflingly incompetent – at one point they send out 40 unmarked cars with plainclothed officers on board, acting as bait “to flush out the killer”. Operation Shield doesn’t end in the way they might have hoped (although it might end in the way you suspect).

The Hunter of the Dark is described as a “new Italian literary thriller sensation” by its publisher, but this is, perhaps, more a virtue of how we tend to view fiction in translation – worthy, rather than fun – than any claim to literary heights. It’s more Stieg Larsson than Henning Mankell, more Jo Nesbø than Karl Ove Knausgaard, and none the worse for it – conspiracies abound and evil blossoms in Carrisi’s version of Rome, “a place where every revealed truth hid another secret, the whole of it wrapped up in myth”, a city whose “greatness… had been fed with blood”.

And the penitenzieri and the “archive of sins” they have collected from the worst of the confessions made to priests over the centuries are a gift of a storyline; in an author’s note at the end of the novel, Carrisi writes how they are, actually, real – the oldest ministry in the Vatican, they even, prosaically enough, have a website. So while there’s a little too much going on here, it’s largely down to the author’s excitement at his topic: “How is it possible that nobody has ever written about the penitenzieri? What a terrific subject for a novel!” he tells us in glee. And it makes for a gallopingly fun read: dark, disturbing and teetering blissfully – and, mostly, knowingly – on the brink of the preposterous.

Hunter of the Dark is published by Abacus (£12.99). Click here to buy it for £10.39