In November 2010, a stoat (Mustela erminea) was sighted on Kapiti Island, a mammalian pest-free nature reserve 5.2 km off the Wellington coastline. Its presence was confirmed using DNA recovered from a scat that was located by a dog accompanying an incursion response team. Over the following 18 months, three stoats were trapped, and numerous scat samples and bird carcasses were collected. These were analysed using both molecular and morphological techniques to confirm the presence and activity of stoats on the island. Five out of nine scats originated from stoats and the death of one of six killed birds was attributed to a stoat attack. Data showed that the three stoats were very likely to be related to each other, with the first, a female, being 1 year older than the other two, and their probable mother. The other two stoats (a male and a female) were born on the island in 2009. Despite trapping and detection efforts continuing until February 2013, the last stoat scats were found in October 2011. Evidence suggested that the founder stoat reached Kapiti Island by drifting and swimming from the mainland.