Detained is one of those episodes rather common in science fiction series where people act against type or act angry because of an alien presence such as in the Doctor Who episode, Midnight.
Here we get a claustrophobic episode set in a classroom as the students are put in detention by Miss Quill who locks the room and promptly leaves for an hour.
A fragment of a meteor crashes into the classroom taking them out of normal time and space. Matteusz picks up the rock and it becomes something like a confession device as Matteusz tells Charlie that he loves him but is also afraid of him, but we have seen this in a previous episode that Matteusz is suspicious about Charlie's motives regarding the hidden cabinet of souls.
Others take turn in holding the rock and revealing their true feelings, they are apprehensive, angry, bitter, afraid and there is something more to the meteor's entity than they initially thought.
Episode 6 is the calm before the storm of the final two episodes, allowing room for character development, a small scale episode. I am not sure that the young actors were up to the mark for this kind of intense drama. I do not think Patrick Ness's script delivered, it was rather boring and derivative. Teenage angst on show but it all felt hollow.