Watson's keen interest in learning to sail prompts Holmes to take a rare break from Baker Street. Arriving in Lymington, Holmes intends to instruct Watson in the finer points of sailing. However, this is thwarted when Holmes falls desperately ill and poisoning on a grand scale is suspected. As Holmes recovers, Watson is tasked to gather evidence and a visit to his aunt exposes the true extent of the horror. Holmes's deductions and a reminder of Watson's embarassing exposure in old case inspires Holmes to present a chemical solution.