The net is closing on an anonymous writer with a "poison pen" sending letters to residents of a small South Island town.
Senior Constable Helen Fincham-Putter said three anonymous letters about Middlemarch residents have been written with a "poison pen".
"We have a right little busybody in town."
Two letters were sent to two separate wives and gave "unwelcome advice" on the "state of their marriages".
"If you think someone needs to know that information, you should be able to tell them face-to-face, otherwise it's just gossip and you should just keep your beak out," Fincham-Putter said.