A woman was stunned to return home and find 107 gnomes carefully arranged in her front garden.
Police were called at about 1.30am on June 2 after Marcela Telehanicova found the gnomes, including a formation 30 rows deep and three abreast.
Officers are now investigating the incident, which took place at Bowdens Park in Ivybridge, Devon, between 9.30pm on June 1 and 1.30am the following day.
Writing on Facebook, Ms Telehanicova described some of the gnomes as "creepy looking".
"Okay who has put 100 gnomes outside my front door?," she asked.
"Funniest thing I have ever seen. How am I supposed to go to sleep now?
"I don't know who has done this but I want to thank them for giving me the best laugh ever. I have no idea whether they got the wrong house or just randomly picked mine but I am so glad they did."
A local garden centre has been checked but no gnomes have been reported missing, a spokesman for Devon and Cornwall Police said.
The incident is being treated as "found property" and residents are being urged to check their gardens to see if any gnomes have disappeared.
"Someone has taken quite a bit of time and effort to place them there," the force spokesman said.
"It has unsettled the home-owner who has no idea why they were put in her front garden at night.
"We are seeking to establish where the gnomes have come from.
"The question is whether they are stolen, or if it's a prank and someone is playing a game of gnomes."
Anyone with information is asked to contact the force on 101 quoting police log number 27 of 2/6/2015.