MYSTERY BOOKS I WOULD HAVE LOVED AS A KID

I read a lot of mystery books as a kid, but I wish they had been a little more, oh, I don't know... Here are some blurbs for books I think I might have liked:
  1. The Bobbsey Twins and the Red Brigade
    On a family vacation to Italy, Freddy and Flossie get separated from the rest of the family and end up getting kidnapped by the Red Brigade. While their parents work with the Carabinieri to try to get the kids released, Bert and Nan do a little sleuthing of their own. With a little help from some street urchins they meet in the alleys of Turin, the twins manage to turn the tables on the captors, and the family is happily reunited.
  2. The Hardy Boys: Low Rent Rendezvous
    Frank and Joe Hardy are getting ready to help Aunt Gertrude move some stuff out of the attic when they get a frantic call from chum Chet Morton. His sister Iola is missing! They find her diary in which she describes her excitement at her new modeling career, and the mysterious stranger she met Saturday night at the roller-rink. They learn of her plans to meet with him in a seedy part of town. Will they find her in time?
  3. Nancy Drew: The Clue on the Doorknob
    Nancy Drew decides to drive to Emerson College one weekend and surprise her boyfriend, Ned. Nancy knocks on Ned's door, and thinks she hears muffled voices inside, but Ned doesn't come to the door. She notices a necktie on the doorknob, just as Ned's roommate Ben appears in the hallway. Ben looks from the doorknob to Nancy, and quickly rushes her to the Student Union for coffee. Ben assures Nancy that everything's fine, but she is suspicious, and vows to get to the bottom of the mystery.