Sherlock type TV Show network PBS genre Crime

Sherlock‘s newest mystery: The case of the missing viewers!

Season 4 returned to 3.7 million viewers on PBS Masterpiece on Sunday night, dipping from the third season’s record-setting 4 million viewer premiere two years ago. That slump trend echoes the UK premiere, titled “The Six Thatchers,” which debuted to 8.1 million viewers overseas — down 1.1 million viewers from season 3.

The PBS premiere was up 7 percent, however, from last year’s “The Abominable Bride” special (while the UK telecast was down a bit from the special). Normally the top suspect would be the episode’s timing — as airing on a holiday weekend tends to depress viewership — but season 3’s record-holding premiere likewise aired on New Years’ Day.

Season 4 continues with “The Lying Detective” on Sunday, and concludes with “The Final Problem” on Jan. 15. For more, check out our interview with showrunner Steven Moffat discussing the shocking ending to “The Six Thatchers.”