Could it have been Mrs Ralston in the library, Major Metcalf in the dining room or Mrs Boyle in the kitchen?
Well - it could be any of them and the only way to uncover the murderer is to go along to the Sunderland Empire and find out.
The daddy of whodunnits - Agatha Christie's The Mousetrap - is being staged at the city theatre and looks to be proving as popular as ever.
It's a freezing night and the guests at Monkswell Manor Guest House have gathered to take refuge against the storm.
All roads are blocked by the snow and it is obvious that no-one is leaving anytime soon - if ever.
The legendary crime drama will run at the Empire until March 2, and this production stars Gwyneth Strong of Only Fools and Horses fame, as Mrs Boyle.
The actress, who played Cassandra, the long suffering wife of Rodney, puts in a great performance as the prickly Mrs Boyles, who is generally annoyed with everyone and everything.
This unstoppable West End hit has been delighting theatre-goers for 67 years with its macabre murder mystery.
Following a record-breaking 60th anniversary debut tour in 2012, this timeless thriller has returned by popular demand for an extensive new tour that will
travel the length and breadth of the country giving audiences all across the UK the opportunity to discover theatre’s best kept secret.
Strong is joined by a great cast of actors, who put in sterling performances in this edge of your seat play.
It's difficult to talk about The Mousetrap without giving anything away - and audiences join a pact to keep the murderer a secret.
But, it starts with young couple Molly and Giles Ralston, played by Harriett Hare and Nick Biadon, who are preparing to open their guest house to its first ever visitors.
One by one, the mixed bunch arrive, battling through the blizzard, and the staging is so realistic that you can practically feel the cold of the storm outside.
Guests include the eccentric Mr Paravicini, played by David Alcock, upstanding retired military man, Major Metcalf, played by John Griffiths, Mrs Boyle, strange and larger than life young man, Christopher Wren, played by Lewis Chandler, and mysterious young woman, Miss Casewell, with Saskia Vaigncourt-Strallen in the role.
They are joined by Det Sgt Trotter, played by Geoff Arnold, who has skied through the snow to warn the guests they are in danger.
Everyone in the house seems to be harbouring secrets, but what could lead to someone being killer - or to kill.