At the end of World War II, tens of thousands of tons of chemical warfare agents - mostly mustard gas - were dumped in the Gotland Deep - a deep basin in the middle of the otherwise shallow Baltic Sea. Decades later, these weapons are being reactivated - both literally (perhaps on the faces of dead seals, and in fishermens nets) and also in our imaginations. In this story that recounts the beginning of our research into this situation, militarization meets with environmental concern: the past floats into the present, where humans and non-humans are equally implicated, where the sea itself conditions the kinds of questions we can ask, and answers we might get, and where terms like threat and risk remain undecided. After spending time on Gotland Island - the closest terrestrial site to these weapons dumps - we ask what kinds of research methods might be adequate to these tangled, underwater tales that we find so difficult to fathom.