Wow. This book was absolutely captivating! From the moment I started reading, I couldn't put it down, devouring it in just two days, as stated by Goodreads reviewer Natasha Mayston. However, Natasha wasn't expecting anyone to knock on her door so late at night, and she had no idea that the face staring back at her would be the last one she'd ever see.

As Detective Dan Lockhart is called to investigate Natasha's death on a wealthy London street, he's startled by the similarity to a previous case. Noticing the cable-tie restraints and the tiny scratches on Natasha's wedding finger, Dan already knows what he'll find if he looks in her mouth – the metal ball that choked her to death. He realizes Natasha isn't the killer's first victim and is certain the perpetrator will strike again.

Months earlier, Kim Hardy was found in the same position in a run-down hotel across the city, with an identical silver ball in her throat. But Kim's murderer was caught and sent to prison, leading Dan to wonder if they arrested the wrong man. Fearing he's dealing with a psychopathic serial killer, Dan calls in psychologist Dr. Lexi Green to help him get into the perpetrator's mind.

Tough and smart, Lexi is determined to stop at nothing to hunt down the man responsible for the deaths. Then, another body is discovered, just as Lexi finds a clue online leading to the killer. Dan's team isn't convinced, but in pushing Lexi away from the investigation, they force her to dig further into the case on her own. Convinced she's on to something, she puts herself in unthinkable danger.

Can Dan piece together the clues and identify the killer before it's too late? Fans of Angela Marsons, Robert Dugoni, and Cara Hunter will love this thrilling new series from Chris Merritt. From an explosive start to a heart-stopping finale, you won't be able to put this book down.

What readers are saying about Knock Knock:

"Gripping from the get-go... Impossible to put down once you start... The fact that I kept turning the pages, the adrenalin pumping, makes Knock Knock a compelling read." (Goodreads reviewer, 5 stars)

"My heart beating so fast! I couldn't believe what I was reading. It had me in shock. Every page, every chapter was a page-turner... What a rollercoaster." (Goodreads reviewer, 5 stars)

"Oh wow... I am a huge fan of this author's work... These are the books that I love!... This book is just great, greater, the greatest!" (B for Bookreview, 5 stars)

"Loved the book. It's edge of your seat reading." (Goodreads reviewer)

"Wow! This is one of the best books I have read this year. Really incredible!" (Goodreads reviewer, 5 stars)

"Oh, this was good, very, very good... I was blown away... It's one hell of a good thriller." (Goodreads reviewer)

"I fell into this story and finished it in two days... A must read." (Two Girls and a Book Obsession, 5 stars)

"My heart was in my mouth... I loved it." (Goodreads reviewer, 5 stars)

"What a roller coaster!... Like OMG!... It's so good." (Goodreads reviewer, 5 stars)

"An absolutely gripping and fantastic read." (NetGalley Reviewer, 5 stars)

"The ending is brilliant and full of suspense." (Goodreads reviewer, 5 stars)

"I was completely immersed in the story, the suspense had my heart pounding at times. This is an unmissable and intense thriller." (Goodreads reviewer, 5 stars)

"Tense and chilling with so many twists and turns." (NetGalley reviewer)

"I literally couldn't put it down." (Book Lover, 5 stars)

"A fast-paced thriller with a jaw-dropping finale." (Goodreads reviewer, 5 stars)

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