There is no episode of Vera titled "Aiff." However, there is a Season 5 episode titled (S05E02) and a Season 6 episode titled "The Sea Glass" (S06E04). It is possible you are thinking of "The Sea Glass" or "Changing Tides."
One of the standout aspects of this episode is its thoughtful pacing. The writer(s) take their time to develop the characters and their relationships, which makes the subsequent revelations all the more impactful. Vera, in particular, is given some wonderful moments to shine, showcasing her keen instincts and sharp wit. vera s05e01 aiff