The sign of the five

"In the second thrilling installment to the Improbable Tales of Baskerville Hall series, Arthur returns to the elusive Baskerville Hall and must solve the mystery behind a poisoned Sherlock Holmes, facing new threats, harrowing challenges, and ghastly ghouls along the way. It's time for a new adventure, are you ready? When Arthur Conan Doyle returns to Baskerville Hall, a secretive school for extraordinary students, he's excited to begin winter term with the friends he loves. However, soon after his arrival, a dangerous foe threatens his favorite professor, Sherlock Holmes, and all signs seem to point to a force that Arthur had hoped he'd seen the last of ... the Green Knight. But Sherlock isn't the only target; others begin to fall prey as well. The question is: how are they all connected? In the ultimate race against time, Arthur will have to dodge old enemies, befriend new faces, and brave encounters with spirits to solve the mystery before it's too late. But there are more puzzles to solve than one; it seems a new term at Baskerville Hall may not only test Arthur's wits ... but his friendships too."--