This Code Blue Special connects the first Season of Code Blue with Season 2.

It tells the story of the first Season further so I highly recommend to watch Season 1 first as this is not a stand-alone movie.
After the happenings of Season 1 the four interns return to the hospital and are called to a derailed train with lots of injured. There's one scene with a young boy that even I (who is used to watching medical dramas/movies) find quite intense.
I won't give away anything else but I enjoyed this story very much because we get to see a character growth of the interns if you compare the early episodes of Season 1 with this Special.

The cast is the same as in Season 1 and does a really good job.
The music is not changed in this Special which I personally appreciate as I find the OST totally fitting.

Rewatch value is high because I like the cast and story a lot.

Overall I enjoy this series a lot and recommend it to anyone who's looking for a good medical drama. With 3 Seasons and Specials there's a lot of things to keep you entertained.