There are plenty of intros. Here are some:

Baldi, Philip. (1983). An Introduction to the Indo-European Languages.

Beekes, Robert S. P. (1995). Comparative Indo-European Linguistics.

Mallory, J.P. (1989). In Search of the Indo-Europeans. [More archeology and anthropology.]

Mallory, J.P. (2006). The Oxford Introduction to Proto-Indo-European and the Proto-Indo-European World.

Some may be out of print and can be found used.
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Ceci n'est pas un seing.