Smother star Seána Kerslake has told RTÉ One's Today that she thinks fans will be "surprised" by the big reveal in the whodunnit on Sunday night.
The Dubliner, who plays Grace in the mystery, joined Rachel Allen and Dáithí Ó Sé on Tuesday as the countdown to the final episode continues.
Although she said that she thinks fans are in for a land when all is revealed, Kerslake was giving little else away.
"Soon enough, you'll find out," she teased. "Come Sunday evening, you'll know."
"I wonder did she do it, did she?" asked host Ó Sé.
"No, she didn't," replied co-presenter Allen. "She definitely didn't."
Fans can find out on Sunday on RTÉ One at 9:30pm.