Officers were called to an address in Fleet Street, Holbeach in the early hours of Saturday morning.
A 14-year-old boy was found dead at the scene and his family have been informed.
A 15-year-old girl and two 19-year-old men were arrested on suspicion of drug related offences and have been released on bail.
A police investigation into the circumstances is ongoing.
To report information to officers please call 101 quoting incident 34 of 6 April.