Staying in pub - landlady's daughter comes back from playing on the beach in the early morning to collapse - initial thoughts are that she's ill, further investigation will reveal she's been poisoned.
Turns out the kids (small group on beach) found a rowing boat aground, with a case in it. They nicked the case, found it was full of food, and eat it several die, all very ill (they didn't eat much of the food 'cause they didn't like it - unusual taste).
Food was being dropped off to be picked up by a caravan passing nearby, where it would be swapped for an identical case (unpoisoned) and sent on to its buyer, a powerful alderman (or equivalent) in a nearby town.
So - to help out the landlady the PCs have to sort out a number of things owner of the boat, realise a caravan was going to be nearby at the time, find out from the merchant where the food was going, make all the right connections. They should then meet up with the alderman, who'll realise the attempted assassination attempt (especially if the PCs have still got a sample of the food - its a delicacy that's his favourite and that no-one else likes), and may ask the Pcs to sort out who was behind the poisoning. This will now entail crawling around the city getting the poison analysed, tracing the boat, the buyer of the poison and so on. Who's behind it is up to you (as is everything else really) - I had his son responsible (via a long and convoluted chain.)