Hence I have attempted to create "Theme from Unknown Man", the title sequence from a little-known TV series shown for 3 weeks only on ATV Midlands in 1969.
In my simplistic way, "spy theme" boils down to semi-tone intervals and lashings of plate reverb. So I fiddled around in Am and added grace notes a semi-tone above or below where the main notes were until I got a melody that sounded suitably mysterious. I played the first half in 3/4 across the 4/4 beat to make it sound interesting, and the second half in 4/4, but shorter phrases, to make it sound like it was going faster.
Production wise, this was straight into the audio interface and all effects in the box: JS 1175 compressor (one of the many compressors in Reaper), a bass amp plugin that came free with Computer Music, TAL's Dub II delay, Acon Digital Verb (also free with CM), and a (free) valve exciter thing to sprinkle a little pixie dust over the top. (I haven't gone for many paid plugins yet!)