I think we're dealing with another case of alien abduction, chief. Tiny, vulnerable seedlings disappear from a third floor windowsill? Not a trace of them on the street below? No sign of forced entry? Aliens, man.
(Oh but all is well-- we are a resilient duo. We adopted some seedlings from our local farmers market and are watching them carefully. My nan suggested that I make a missing plant poster and I couldn't resist.)