The opening credits are slightly altered to include the character of Adam, implying that he was a member of the team from the outset.
This is the first time we are privy to some of Jack's back story and who Gray is (first mentioned in Episode 2.1, Kiss Kiss, Bang Bang (2008)).
While filming the kiss between Captain Jack and Ianto, director Andy Goddard deliberately didn't call "Cut" as a prank so the two men ended up kissing much longer than originally planned.
This episode takes place in 2008 and the 51st century.
Burn Gorman (Owen Harper) and Bryan Dick (Adam) appeared in the same episode of "Marple", Ordeal by Innocence (2007).