In the previous episode, newcomer Charlie accepts Kate's offer to move into her spare room just before Christmas. This one is obviously set in the springtime, given the prevailing weather, including a river nearing flood levels. Yet Charlie tries telling Barnaby about how surprisingly messy Kate's place is, as if he'd just moved in. That either leaves him homeless or comatose for several months between the two, since his professional powers of observation would not allow him to have remained that oblivious for that long.
When DCI Barnaby comes to Professor Philip Hamilton's home after he is murdered, it appears to be raining hard. But the sun is shining brightly, revealing that the "rain" is contrived by crew members. This happens again in two subsequent scenes.