351T: Young boy with red/brown hair and glasses solves mysteries using science

One book cover includes him on the cover with a lab coat and beakers. The cover may have been blue or purple. It was very block cartoonish. He solves mysteries with a girl who is also on the cover with a lab coat on. They may have had a dog. I believe they solved mysteries in their apartment complex or school. It was a series that may have been Scholastic as I believe I got it from a book fair as a child. The book would have been out in the early 2000s.

350D: Shannon’s Job in the Historic House Run by Two Sisters

Years ago, I read a mystery about a college student named Shannon getting a summer job at an old house run by two old ladies (sisters). Students dress as Gibson girls & do tours through the historic house. Shannon befriends another girl student. There’s a guy that took a summer job there too. He’s a writer, I think his name is Michael. A relative of the Sisters also lives there. She likes caramels. There’s a murder. I think the Sisters names are Cora & Lanie or maybe Lennie.

349O: Children Look for Missing Mother, Who Got in Accident

A young mother leaves her children to go for a romantic night away with her boyfriend. She realised her mistake and rushes home but is in an accident.
The children are unaware but continue going to school pretending all is OK. They go on a school trip near the location of her night away and look for her. They also have an accident  and all are reunited at the hospital.

349M: The Empty Valley Mystery

All I remember about this book is that a group of kids (who were maybe related. There were two brothers?) ended up in this absolutely empty valley - there was a plane involved. And they explore this valley - find a cave to live in. And at some point they solve a mystery - a chicken is involved - and they find gold. And then get rescued. This was is the Hardy Boys/Nancy Drew genre. All I remember about the cover is that it had a numeral of sorts on it. Also, in another book in the same series one of the brothers finds a rare bird - a great auk or something.

349B: Man disappears from London, found years later in French circus (Solved!)

I think this was an English mystery or part of one, maybe from the Golden Age of mysteries (Christie, Allingham, Sayers?) where a City man leaves his home to go to work, is seen by a tradesman at one end of a block, but never reaches the other end and is never seen again. Much publicity about his disappearance. Years later, someone — perhaps a young relative — finds him as part owner of a small circus in France, with his partner the neighbor woman with exotic snakes whose high brick wall in the middle of the block he vaulted over to live with her.

348W: Who Kidnapped Toddler?

British psychological thriller, probably 2019. Small child disappears from yard while young mother carelessly supervises her playtime.  Meanwhile, a married woman is in  a relationship which begins to reveal itself as rather strange and secretive. Her evasive husband becomes a suspect when coworker points finger in his direction, but his alibi is that his delivery route is far from the kidnapping site. Clues and suspicions build until his wife can no longer avoid suspecting his cagey behavior and question his guilt.

348P: Island Mystery

Main Character is a young woman hired to be a companion to a teen by the teen’s guardian. Takes place on an island that you have to take a ferry to the mainland. The teen goes missing and the guardian’s younger brother says she ran away and he cuts off his hand to cover up the murder scene. There is a scene where they make oatmeal by leaving it on the stove overnight. The companion starts to be attracted to the younger brother but discovers what he did.

347R: Kids hunt for a treasure at a lake only to find it’s confederate money

I read the book in grade school in the early 80's.

I remember it's a mystery book where kids visiting a lake look for a treasure.  In the end, the treasure turns out to be worthless confederate money.  One scene I remember vividly:  The boy is tricked by the girl to swim to the bottom of the lake with his snorkel and look up.  She claims it's a beautiful view.  When he does so, the protective valve on the snorkel opens and water floods into his mouth.

I also seem to recall a dragon on the lake at night, but it's made of paper and burns up from the candles used to illuminate it.  It is possible, however, that this memory might be from another book...

346P: Teen Mystery Centered Around a Library (Solved!)

It’s set in a small town where the main girl is a young teen/pre-teen and she lives with her grandparents and her uncle who is younger than her and is basically her little brother. They go to the library in town (the mystery of the book is centered around the library) and the library has a large mural of Andrew Carnegie burning in hell because the town hated him and refused one of his Libraries and built their own with a big “f you” to him in it.