Arden Blake #3 Missing at the Marshlands by Cleo Garis

In Missing at the Marshlands, Arden, Sim, and Terry stay with Terry’s mother in Oceanedge.  A Russian painter stays in a nearby houseboat, and he has several mysterious visitors.  When the man vanishes, the girls begin looking for him. Meanwhile, the girls also hope to help an underprivileged girl named Melissa who lives in the area.  Melissa is mistreated by her father, and the girls want to help her.

I found it interesting that the girls tan on the beach and use tanning oil.  I don't know that I have ever read a vintage series book from the 1930s where the girls actually tan on the beach.

From page 67:

"Looks to me as though we've dropped right into the middle of another mystery," Terry announced, nodding her read wisely.  "Maybe there are always mysteries, but only wise girls really discover them."

This is a good book.

A. L. Burt books can be bad due to little care in proofreading, but this series is a solid one.  It is better than many Burt series, although it is not one of the outstanding ones.