Well, it depends on the actual subject you want to approach and the "decent command of modern algebra" already assumed; without knowing more, I would recommend:
Number fields (1995) by Marcus. Universitext. Just as the title says, a (great!) introduction to number fields.
Algebraic Number Theory (1986) by Cassels and Frölich. Academic Press. It explains the basics (class field theory, zeta functions) to understand the Langlands Program.
A course on arithmetic (1996) by Serre. Graduate Texts in Mathematics. P-adic fields, quadratic forms, zeta functions and modular forms.