4. The clue is the first line of Browning's poem The Pied Piper of Hamelin, where the city is invested by rats. The council offers a reward for anyone who can get rid, and up comes the Pied Piper. He charms away the rats, but the council refuse to pay him, so in revenge he charms away all the children from the town.
So, are we looking for the collective noun for mayors, councillors, pipers, rats or children?