"Stabbed under the left shoulder-blade while she was singing."
"Singing! What was she singing, and why in a strange house?"
"She was singing 'Kathleen Mavourneen.'"
Laura looked surprised. "My sister's favourite song."
"Oh indeed," said Derrick sharply. He hesitated. "Your sister is also at Westcliff-on-Sea?"
"Are you about to accuse her?" asked Laura disdainfully.
"I accuse no one," replied Derrick, nettled. "I am only trying in all directions to learn facts upon which to build up a theory."
"Then why don't you look for real evidence?"
"Such as what, Miss Mason?"
"Such as the weapon with which this woman was killed."