The Headley Cross marathon has been held every year since it was founded in 1983. This time, as well as the full run, a half marathon is being offered, and preparations are well under way. DS Zander Ellery and DC Isabel York have a hectic caseload and could well do without the squad having to run the marathon. When the race is threatened, they and the other members of the MIU/Major Crimes are tasked with neutralizing the threat. As the day of the race draws near, with ten thousand runners due to take to the streets, time to find the culprit is running out. Lives are at stake, and Ellery and York must succeed in winning this race. —Part 1 of the SEE HOW Ellery & York sub-series