《摩斯探长前传》第四季于2017年1月回归ITV，本季共四集，标题分别为《游戏》、《圣歌》、《检疫》、《丰收》。剧情以1967年为背景，承接第三季结尾，由Shaun Evans和Roger Allam主演，Russell Lewis担任编剧，摩斯探长系列小说作者Colin Dexter担任顾问。

Outside Parliament in Reykjavik, a man throws himself at the Minister for Industry, setting fire to them both. He dies, but she survives. Andri Olafsson, now working in Reykjavik, is assigned to the case.