The unclued lights consist of one author, two titles and four characters; ignore one accent. The titles (three words and five words) are pairs.

Across

6 50% caught in large-scale disease outbreak (8)
12 Get everyone out of Aleppo, due to lunatic taking over (10)
13 Rolls makes an impression (9)
14 Killer gets into motor car (4)
15 Wherein somehow I see the cold? (8, two words)
17 Vagrant’s absolutely not bonkers (5)
21 Eccentric work about witch being an old ass (11)
22 Isn’t conscious, so zones out (7)
24 Who supplies seashells essentially? (3)
26 Aim for boundary (3)
28 Geneticist analysed sockeye salmon, not finding mace...