On a rainy April day, an old school friend of Theo's comes seeking help from the Milestone Agency. Simon Cordell has found himself accidentally involved in a romantic triangle, an awkward situation that turns to tragedy when one of the parties is found drowned in the Thames. Theo and Rose agree to try and clear Cordell from suspicion, but with flood waters threatening to engulf Oxford, the duo find that for once, they may be in over their heads.

'Oxford Aqua' is the sixth novel in the Milestone Agency Victorian Mystery series.