Another

As the anime is airing this season and I'm too busy and/or lazy, get your summary somewhere else, but not on Wiki as that one already tells you a third of the whole novel.

緋色の囁き

Being related to the principle's family tree and therefore taken from her adoptive parents, Izumi Saeko becomes a transfer student of the reputable Seishin Girls' Academy and starts living in its dorm. Her roommate Takatori Kei seems like a kind person to get along with, but Kei herself thinks it would be better for Saeko to not get involved with her, leaving her with the mysterious statement "I'm a witch" before she is found burned to death in a forbidden room of the dorm where another girl died the exact same way 35 years ago. From that night on fear and suspicion prevail among the students and what was regarded by the teachers as possible suicide finds its continuance in clear murders afterwards. The scarlet whisper crawling up from Saeko's forgotten inner self and her continuous sleepwalking and strange dreams make her doubt herself. Might she actually be the culprit...?

霧越邸殺人事件

On a late autumn day dramaturge Yarinaka Akisaya, his 7 actors and his friend, the novelist Rindou Ryouichi, have to take shelter from a snow storm in a western mansion that suddenly appears from the depth of mist that ascends from a lake. They don't seem to be welcomed by the inhabitants but each get their own room designated. Even so they are continuously reminded by the servants that Kirigoe Mansion is not a hotel and that they shall not sneak about too much, especially they shall not enter the 3rd floor at all...

In this ominous mansion strange coincidences happen and the building itself is said to be a mirror that reflects the future of those who visit it. Little would the guests be able to guess how these occurences lead to a chain of murders after the mansion and its surrounding are totally covered by snow without any way to inform the outer world...

人形館の殺人

Hiryuu Souichi moves into the mansion his father left behind after his suicide. The several mannequins standing around there count to the lesser mysteries Souchi encounters in his new environment. Strange sounds at night, threatening letters and the staring gazes from the neighbourhood and eventually a murder incident drive Souchi into calling Shimada Kiyoshi, an old friend of his to make sense of the strange happenings that begin to entangle him.

迷路館の殺人

Prominent mystery writer Miyagaki Youtarou invites his 4 disciples, a literary critic, an editor and his wife and mystery maniac Shimada Kiyoshi to his underground labyrinth mansion. However he is found dead when they arrive and a tape tells his disciples of his wish to improve their skills under the condition of being locked into this closed circle situation and write themselves into their works using his mansion as location. Their works are to be evaluated by the critic and the editor and the winner is going to inherit Miyagaki's entire fortune. The authors begin to write their individual stories and it does not take long until murders happen according to those scripts.

This incident became fairly known afterwards and one year later a literary reconstruction published by Kitansha Novels arrives at Shimada's. It was written under the pen name Shishiya Kadomi, who claims to have been involved in the case, which Shimada acknowledges before he delves into the book...

水車館の殺人

The odd-looking 'water wheel mansion' inhabited by a masked host and a lonely young woman... Last year in a stormy night it was haunted by an unfathomable tragedy. Will the nightmare occur this year again? The secret of Fujinuma Issei's posthumous visionary painting and the mysterious disappearance of Shimada Kiyoshi's friend from a locked room guides Shimada to the mansion to uncover the secret truth hidden behind the steadily turning water wheels...

十角館の殺人

Tsunojima, Aoyashiki's burnt down remains and a decagon-shaped guesthouse. The latter is used by seven students from a university's mystery club and as someone would naturally expect considering this setting, serial murders start happening on this otherwise uninhabited island with no one willing to confess the crimes. Two other students who did not visit the island with their fellow students receive mysterious letters from Nakamura Seji, the proprietor of former Aoyashiki and the whole island, who supposedly died in the incident in the mansion half a year ago. They find out that those letters were also sent to their meanwhile absent fellow students and they begin investigating the incident of Tsunojima's past...