The episode opens with Ada having a barney with nosey neighbour Mrs Chandler. A character never seen before and not seen again after this.
The main thrust of the episode is Ada has sent a birthday card greetings to the Queen and she expects a personal reply.
Walter gets Leslie to add personal note to the bog standard reply from a royal secretary. Only for Leslie to add that Ada should drop in if she was passing Buckingham Palace.
So Ada decides to do just that leaving Walter worried.
Another gentle episode although you sense it was a bit much for Leslie to invite Ada to drop in to Buckingham Palace. I guess that was the main plot. A good job that Ruth can spot her husband's handwriting.