Once you're all done with your errands inside Minette's studio, its time to tackle the things on your to-do list. If you haven't yet, go look at the to-do list on Nancy's computer. Then try and head out the door - doing so will result in a piece of letter being slid under the door. Pick it up and open it. You'll find the Minette has received apparently, yet another threatening letter from an anonymous person! Heather will ask you to place the letter inside the Dodo box in the office. When you're done, you can work on your to do list in the office (the plotter) or the errands you need to do outside.
By the way, conversation with Heather will reveal info about the other characters in the game. It will be interesting to note the connection between Heather and Dieter. Once you're done with idle chitchat, its time to get to work! By the way, Nancy Drew games operate on a time basis, meaning that when it reaches night time, Nancy will have to go back to her flat and rest for the night. Although it might be an inconvenience it really does nothing for the plot.