A Discovery Disappears by Pip Murphy
Book 1 in the Christie and Agatha's Detective Agency series!
Whoever gave you that sandwich did it deliberately. They wanted to sabotage Fleming's research.
When Agatha accidentally eats a major scientific discovery (hidden in a sandwich!), it's a race against time for twins Agatha and Christie to find out who's trying to ruin physician Sir Alexander Fleming's reputation.
About the Christie and Agatha's Detective Agency series:
It's not easy growing up in the 1920s. While Christie can usually be found up a tree or trying a spot of amateur engineering, her shy twin Agatha buries her nose in books and dreams of being a writer. The pair couldn't be more different. But when a scientific discovery goes missing, they find that together they make a winning combination and Christie and Agatha's Detective Agency is born. Join the twin detectives as they solve thrilling mysteries all over the world!