15 letters Take apart in order to reproduce ... or a hint to what's hidden in 17-, 23-, 34- and 46-Across Answer: REVERSEENGINEER
15 letters Long-running western anthology, the only American TV series with its three initials Answer: DEATHVALLEYDAYS
15 letters Literary character played in film by Charles Laughton, Anthony Perkins and Geoffrey Rush Answer: INSPECTORJAVERT
15 letters "Hmmmmm ..." [as hinted at by the three groups of black squares in the middle of the grid] Answer: SOMETHINGSFISHY