Mystery Month in Genius Tangram: Meet Author Mildred Benson and Experiment with Invisible Ink

March 5, 2022 / DIY & Printable

Genius content refreshes every month! This month, dive into all things “mystery,” from unexplained phenomena to the Geniuses who’ve built careers off the genre.

We’ve compiled limited-time game updates, real-life genius stories, and educator-approved activities into interactive printables, designed to enhance your little kids’ learning. Access this week’s printable by clicking the button below:

Game Update

Check out Osmo Tangram for six Mystery-inspired puzzles for kids and new character outfits to unveil. Only available this month!

Genius Spotlight: Mildred Benson

What do “The Secret of the Old Clock,” “The Hidden Staircase,” and “The Mystery at Lilac Inn” have in common? They’re all titles of Nancy Drew books, written by Mildred Benson!

Mildred went to school in Iowa for English and journalism. She worked at different newspapers before applying for a job at a book publishing firm. There, Mildred’s job was to take basic story ideas and turn them into 200-page children’s books.

One of her first assignments was to write “The Secret of the Old Clock,” about the adventures of a teen sleuth named Nancy Drew. Mildred would write 22 more books in this series, including the first 7, but her identity as the author wasn’t made public for almost 50 years!

The Nancy Drew books — 56 in total — were written by various authors under the pen name Carolyn Keene. The publisher used pen names (or “pseudonyms”) because he thought they were more successful. That might have been true; more than 80 million copies of the Nancy Drew book series have been sold.

As the original author, many people credit Mildred for creating the spunky, daring personality that made Nancy Drew such a likable character. Readers everywhere enjoyed following along on her amateur investigations, solving mysteries alongside her.

Real-World Activity: Experiment with Invisible Ink

Try this educator-approved activity at home. This week’s printable (button above) has instructions with photos!

Writing secret messages is fun! To try it at home, gather these materials:

  • ½ a lemon (or ½ cup milk)
  • Cotton swab or paintbrush
  • White paper
  • Cup
  • Heat source: lamp, iron, or hair dryer


  1. Squeeze the lemon (or pour the milk) into your cup.
  2. Dip your cotton swab or paintbrush into the liquid.
  3. Using the wet swab/brush, draw a picture or write a message on the piece of paper.
  4. Wait for the paper to completely dry. 
  5. Ask a grownup to heat the paper up. This can be done carefully with a hair dryer, iron (between two pieces of paper), or non-LED lamp.

When it’s heated, the liquid goes through a chemical process called “oxidation.”  This turns the liquid brown, revealing your message!