Each thematic word is 'cleaned' by replacing one, or in one case two, letter(s) with an appropriate alternative (always the same) to make a new word.
(I have to say that it's most unlike Dimitry to produce such a rubbishy puzzle)
In actual fact they were all on the 'easy' side this week, but I was only joking about Inquisitor (I know you know really !) Perhaps the editors are being considerate because of the postal problems ?