The character Frankie calls Bobby by the nickname "Steve," explaining that she has always thought of him that way for reasons she can't explain. In the original novel she only calls him Steve once, as part of the phrase, "I get you, Steve," which was a somewhat common saying at the time and can be seen in various novels from the early 20th century, including Dorothy L. Sayers' "The Unpleasantness at the Bellona Club" from 1928, and the 1912 novel "Officer 666" by Augustin McHugh. The origin of this saying appears to be lost.
Patrick Barlow, who plays Wilfred Bragge in this version, wrote the screenplay for the last television adaptation of Why Didn't They Ask Evans? (2009), which was episode 4 of Season 4 of Marple.
Lucy Boynton's second role in an Agatha Christie adaptation, the first being Assassinio sull'Orient Express (2017).
The Welsh-language hymn being sung early in the first episode is specifically a chapel hymn, and would not be sung in a church.
Lucy Boynton (Frankie) and Daniel Ings (Roger) previously starred in the same episode (Nocturne (2014)) of Il giovane ispettore Morse (2012), which also happens to be a murder mystery.