A Hamelin researcher is anxious because he's unable to deliver his sister's medicine to her.
This errand is available after completing Errand 055.
The researcher's perils are not yet over, it seems! Pirates in the sea between Hamelin and Castaway Cove are preventing him to bring his medicine towards his sister, so you'll have to take it for him, right? Nope! That would be too easy, now wouldn't it? No... You'll have to kill ALL the pirates on ALL four pirate ships so that the researcher can bring the medicine himself.
Finding the pirate ships is easy; make sure you initiate each fight by approaching the back of their ships to get the upper hand. An All-Out Attack should make it possible for you to wipe out at least one of the three to four Zomboatswains you're up against. The last fight also includes a tougher Cap'n Zombo, so pay closer attention to your health and start using group attacks. You might want to rest in the Cat's Cradle (in Castaway Cove) between battles if you get severely hurt; otherwise these battles are manageable.
Once they've all been defeated, return to the researcher in Hamelin to complete the errand.