Hmm...challenging question since the topic it's asking about, finance, is so broad.
Wikipedia the time value of money, valuation of perpetuities and annuities, modern portfolio theory, mean-variance optimisation, and related topics. Really understand these. Also check out the efficient market hypothesis and behavioural economics. Doing this via Wikipedia is probably better than some pre-packaged finance textbook because it's hard.
Start with bonds: Fabozzi's Handbook of Fixed Income Securities.
For equities first try Pricing the Future - it gives a rare historical context to the Black-Scholes equation. I suppose reading McKinsey's Valuation is good for understanding cash flow valuation. Hull's Options, Futures, and Other Derivatives is the cornerstone piece of the field, followed closely by Paul Wilmott on Quantitative Finance. If you get volatility you understand the liquid equity markets.
Now you understand basic theoretical finance and the entire capital structure (Google that).
Final building block is global macro (not college macroeconomics - you'll need to grab a textbook for that). For this I don't know of a good book. Fortunately, the IMF puts out solid Article IVs, analysts and economists write stuff everywhere, and the Fed, World Bank, WEF, IMF, and a host of other acronyms publish enough data that you can play with to get your feet wet.
From there it literally involves typing things into Amazon, and failing at that, Google, and failing at that, LinkedIn. More Money Than God gives a nice history of hedge funds. The Quants is a fun read of the newer players. You can Wikipedia banks' histories and financial crises.
Go through material because you're curious, not to get through it. Follow your curiosity down branches.
The Quora community has done a lot of good at fleshing out these questions.
I'll second that Quora recommendation. There is a great community there of quants, general hf engineers, MFE students, and others looking to get into the field.
Reading questions within the topics of Trading, Quantitative Finance, and High-Frequency Trading should give you a decent understanding of the basics and provide some good reading materials for beginners.
