Possible Clues:

• Social science classic
• Economist's work I'd ask a pal about — time to get stuck into it
• Composition of red lentils covering offbeat Jamaican-style bread
• Marx treatise
• Marx's masterwork
• Marx work
• Learner after a paid task arranged significant work
• *Karl Marx opus
• 1867 book subtitled 'Kritik der politischen Ökonomie'
• What Marx wrote about the money invested in Germany