A 32-year-old man has been arrested on suspicion of murder following the death of an 11-year-old boy.
The child was taken to hospital after being found unwell at a property in Lincoln just after 10pm on Friday, but died a short time later.
Lincolnshire Police said on Monday that the man had been arrested, and that a woman, 30, had also been detained on suspicion of manslaughter.
The pair are both from Lincoln and remain in custody.
Detective Chief Inspector Richard Myszczyszyn, of East Midlands Special Operations Unit's Major Crime Unit, said: "This is a really tragic incident and my thoughts go out to the family and loved ones of this young boy.
"We have a number of inquiries that are ongoing and we're working hard to establish exactly what caused his death, but I am confident that this is an isolated incident and there is no wider risk to the public.
"This is a shocking and sad case and I appreciate our local communities will be concerned about what has happened and I want to make clear that we are working diligently through the details of this incident and have a number of officers devoted to the investigation."
Information can be reported by calling 101 quoting incident 472 of 22/02/2021, or by emailing email@example.com - with incident 472 of 22/01/2021 in the subject line.