 Sherlock depicts " consulting detective " Sherlock Holmes ( Benedict Cumberbatch ) solving various mysteries in modern @-@ day London . Holmes is assisted by his flatmate and friend , Dr John Watson ( Martin Freeman ) , who has returned from military service in Afghanistan with the Royal Army Medical Corps . Although Metropolitan Police Service Detective Inspector Greg Lestrade ( Rupert Graves ) and others are at first suspicious of Holmes , over time his exceptional intellect and bold powers of observation persuade them of his value . In part through Watson 's blog documenting their adventures , Holmes becomes a reluctant celebrity with the press reporting on his cases and eccentric personal life . Both ordinary people and the British government ask for his help . 
