Board Thread:The Panopticon/@comment-1293767-20151029072618/@comment-5918438-20160122003440

Eh, strictly speaking, Miracle Day could maybe go either way. Each episode has a different director, and produced as separate units, with no production blocks. But remember: all episodes aired as simply Torchwood: Miracle Day, and obviously follow one continuous story, with new linking characters exclusive to that story.

Sounds like a pretty clear serial to me, in a very similar format to the previous serial, Children of Earth. And per "rule 4", one director is not necessary for the designation of a multi-part serial. Sometimes different things are done with serials, as they have many more episodes than a simple two-parter. This, rules 2-3 assume that the episodes in question do not forma concrete serial.