In Nancy Drew: Midnight in Salem, you can make a truth serum and try giving it to people. Several steps are needed to unlock this potion. When you read the last page of Tituba’s book, it mentions the clues to “finding the truth” which include suspected ingredients for “loosening of tongue” and “an unhindered voice” and “to bring forth the hidden thoughts.” Take a look at the herbs in the book on previous pages and identify them:
Loosening of tongue = Rosemary Unhindered voice = Sweet Marjoram Bring forth hidden thoughts = Starwort (Aster)
To unlock the use of these herbs:
Start by looking for the missing key to the box on the counter. The key is located on the display table (see video for exact location).
If Lauren is around, you need to ask her “What kind of herbs to you have?” to gain access to the herb counter. Use the key on the box to unlock Sweet Marjoram.
To find Rosemary, step into the forest past the cemetery and take one step forward. Adjust your view to look left and you will see the bright green cluster of Rosemary. Take some.
To earn Starwort (Aster), talk to Lauren. Choose the “I forgot to mention” option from your dialogue choices to send Lauren to Alicia and get her away from her shop. When she leaves, step up to the herb counter and examine the letter sticking out of Tituba’s book. When you are done reading it, back up and you will get caught by Lauren. Offer to help Lauren with more herbal concoctions, and then complete one full round of filling orders. Once done, Lauren will give you Starwort (known by the new name of Aster) to use in your herb mixes.
Now that you have unlocked all three ingredients for the truth serum, ask Lauren about herbs again to gain access to the herb counter. Instead of filling an order, use Rosemary from your inventory on the mortar and pestle, then add the Sweet Marjoram and Starwort (Aster). If done correctly, you will have a vial of blue liquid added to your inventory.
Step up to every character in the game, and before engaging in conversation, use your vial from your inventory on them to offer the potion, and see what they say!