UK TV series Grantchester season 4 episode 4

A young boy on a farm in the Fens has blood on his hands and is struggling to communicate. As Will starts to talk to the boy using sign language, the pair must come together to help the boy's family heal

with Niall Usher as the boy, Adam Carter

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In the US, now showing on the PBS program Masterpiece (where it is called Season 4 Episode 3). 
My local PBS station offers recent episodes on-line.