ok so @magsbanes post about jocelyn got me thinking (spoilers under the cut)
what if that wasn’t actually jocelyn who got killed? we know valentine has been experimenting with dark shit for years. what if he found out a way to glamour a body to look like someone else, without it looking like a glamour (so the other shadowhunters can’t detect it). this is assuming that regular glamours disappear when a person dies, but maybe they don’t?
so either he just regularly glamoured jocelyn, or it’s some ~special glamour~. point is: the dead body is not actually jocelyn.
instead, valentine has found a way to smuggle her out of the institute, and now she’s being held captive. (there’s a whole discussion to be had here about the absolute fucking horror of her being back with her abuser, but that’s for another time)
now, we know that as of 2x06, luke is still missing since the demon attack (x). what if he saw jocelyn be taken and is out looking for her? alternatively, he’s also been captured by valentine, which could open up a whole new insight into valentine and luke’s ex-parabatai bond. this might even make more sense, because i doubt luke would just bolt and leave clary thinking her mother is dead. it’s still possible that he did leave voluntarily, though, because as he said, "when valentine took you, i promised myself it was the last time i’d ever be without you”. i doubt there was much time to think it through and luke loves jocelyn so much so maybe it’s not that unlikely that he just threw himself into the chase headfirst.
basically, i think there’s a reason we never got to see luke finding out about jocelyn. knowing luke and how attached he is to jocelyn, i think he would be the first person there. i also think there’s a reason we got the first jocelyn kiss in the same episode jocelyn is “killed”. either that’s because they wanted her death to hurt more, in which case it’s shitty writing because there’s nothing admirable about killing an abuse survivor after she’s finally found reconciliation in another love. or it’s a ploy to throw us off, to get us thinking that it’s just done for shock value, when in reality they’re setting up for more depth to valentine’s cruelty, as well as luke and jocelyn’s love for each other.