A nasty stomach bug sweeps through Portwenn and the doctor suspects the local water supply is to blame, taking to the airwaves in a bid to warn everyone. Meanwhile, Al remains determined to leave the plumbing business and attend college, prompting an argument with Bert.

One of Joan's old flames comes back into her life and proceeds to woo her all over again, but Martin discovers the man in question has a life-threatening heart condition, presenting him with a difficult decision. The irascible doctor's problems do not stop there, as a schoolgirl develops a crush on him, leading to a confrontation with her irate father. Meanwhile, romance is also in the air for Al and Elaine.