CSI: Mammy is the 2018 New Year Special of Mrs.Brown's Boys. it aired on December 31st 2017 in Ireland and January 1st 2018 on BBC One in the UK.
When a local church is vandalised, Maria sets up a patrol group to help catch the thieves. Agnes, Winnie and Hillary are all put together by Maria and have a rehearsal in Mrs.Brown's living room with Grandad pretending to be the criminal, but things get out of hand when Winnie acts too nicely, Hillary acts too posh and Agnes, out of her hatred for Grandad, knocks him out with a baseball bat.
Meanwhile, Cathy gets frustrated with several failed dating attempts and thus gets further furious when Agnes lets slip of her dating desires on live radio. which results in numerous men calling at the door showering Cathy with numerous gifts such as flowers and chocolates. Mark also inserts a new door for Agnes, to avoid a draft from drifting since she always left her previous door open. Bono is also furious when his parents won't let him attend a disco for children of his own age group but Mark and Betty later change their minds and let him attend.
At the end of the episode, the culprit is caught when everyone tricks him into going into Agnes' house. Grandad is later treated for his injuries from Agnes earlier by Dr.Flynn, but Agnes refuses to listen when Dr.Flynn says that he is not dying. Grandad then pretends to be Cathy when more men call to door, which thankfully prevents more men from coming to the door.
The episode then concludes with Grandad getting his revenge on Agnes for hitting him with a baseball bat by making her crash through her new door.