A painting worth tens of thousands of pounds has been taken after it was left on a train.
The owner of Terry Frost's 1954 work Blue Harbour was travelling from London Euston to Crewe.
It was left on the train at about 16:00 GMT after they got off at Milton Keynes on 23 January.
The painting, wrapped in brown packaging, is thought to have been removed from the train somewhere between Milton Keynes and Crewe.
Officers have called for anyone with information about the missing painting to come forward.