Secrets of Da Vinci: Monday with a Mad Genius (Magic Tree House #38) by Mary Pope Osborne

The latest entry in Mary Pope Osborne's best-selling Magic Tree House, has just been published. In Monday with a Mad Genius, Jack and Annie travel to Renaissance Florence on another Merlin Mission to discover Leonardo da Vinci's secret of happiness.

When Jack and Annie arrive, however, da Vinci is more perturbed than happy. Trying to perfect a slow-drying oil paint for an important fresco, da Vinci has found that his paint refuses to dry at all. When firepots only succeed in melting his paint and ruining the work, da Vinci seems to be in need of some magical intervention himself. As he shows them his famous notebooks filled with uncompleted projects, the kids decide to use Merlin's Wand of Dianthus to take Leonardo on a winged flight around his beloved city.

His legendary energy restored, da Vinci takes them to his studio for his last appointment of the day, a portrait sitting with a lovely model who never smiles. Under Jack and Annie's gentle questioning, the lady reveals that she doesn't smile because she doesn't want the painting to be completed. When Leonardo assures her that he will never forget her, Mona Lisa brings forth an enigmatic little smile, and the portrait project is at last finished!

And da Vinci's secret of happiness? At first he proudly claims it to be fame, but as his fresco and flying machine fail before him, he realizes that his joy is in his insatiable curiosity!

With the answer to Merlin's query and new knowledge about Leonardo's art and science, Jack and Annie climb into their Magic Tree House and return to Frog Creek, just in time for their first day of the new school year.