of Scorpia and the introduction to Three of Diamonds claimed that Horowitz had travelled to Australia to research a new Diamond Brothers book, entitled Radius of the Lost Shark. This claim was further backed up when a new Diamond Brothers novella entitled The Greek who Stole Christmas! was released in 2007, where it is hinted at the end that Radius of the Lost Shark may turn out to be the eighth entry in the series. However, the next novel in the series was instead called Where Seagulls Dare, and is unrelated to the Australian-based adventure that was previously announced. Horowitz published the first six chapters unedited on his website throughout 2020, and the full, edited novel was published in 2022, with all profits going to support the NHS. Horowitz also published two sequels to his short horror story collection; More Horowitz Horror (2000) and More Bloody Horowitz (2009). Many of the stories in Horowitz Horror and More Horowitz Horror were later repackaged in twos or threes as the Pocket Horowitz series, while More Bloody Horowitz was later reissued as Scared to Death. One of the short stories in More Bloody Horowitz is notable for serving as Horowitz's opportunity to get even with fellow author Darren O'Shaughnessy, more commonly known as Darren Shan. In 2008, the pair had gotten into a joke dispute over O'Shaughnessy's use of Horowitz's name for an objectionable character (Antoine Horwitzer) in Wolf Island. In retaliation, Horowitz chose to plot a gruesome literary revenge in the short story The Man Who Killed Darren Shan. In 2004, Horowitz again attempted to branch out to an adult audience with The Killing Joke, a comedy about a man who tries to track a joke to its source with disastrous consequences. The book was not very successful, and in August 2005, Horowitz returned to young adult fiction by releasing a book called Raven's Gate which began a second successful series entitled The Power of Five (The Gatekeepers in the United States). Based heavily on one of his earlier novels entitled The Devil's Door-Bell, each of the first four entries of The Power of Five subsequently ended up being a rewritten and expanded version of their respective counterpart from the Pentagram series. The second book in the series, Evil Star (based on The Night of the Scorpion), was released in April 2006. The third in the series is called Nightrise (based on