Complex sentence: The last time Slater is seen is in the series finale "Sleepless in Peckham", in a photo of the original Jolly Boys Outing to Margate in 1960.
Split into simpler sentences: The last time we see Slater is in the series finale "Sleepless in Peckham". We see a photo of the original Jolly Boys Outing to Margate in 1960.