It's no secret.
Mrs.Henshaw herself tells of it everywhere.

It was her friend, Alice Greggory, who told me of it first, however.

It seems the cook was gone, and the mistress had to get the dinner herself." "Yes, I know that." "But you should hear Mrs.Henshaw tell the story now, or Bertram.
It seems she knew nothing whatever about cooking, and her trials and tribulations in getting that dinner on to the table were only one degree worse than the dinner itself, according to her story.

Didn't you--er--notice anything ?" "Notice anything!" exploded Calderwell.

"I noticed that Billy was so brilliant she fairly radiated sparks; and I noticed that Bertram was so glum he--he almost radiated thunderclaps.