One of a very tiny number of monographs on the ritual(s) of evocatio deorum - calling out the gods of the enemy.
Gustafsson seeks to analyze what we do and don't know about this tradition, contextualize the theologies of the sources, and assess the impact of the "myth of evocatio" (both ancient and modern).
Parts of this book were very interesting to me, parts felt like I was reading another Mary Beard book (i.e. "We know very little about this, and can never get at the "true" ritual or its "origins").
Gustafsson's most interesting sections deal with identifying an accurate definition of "evocatio deorum" (one that accounts for all the evidence, but doesn't interpret earlier evidence on Macrobius) and when she analyzes the theological impact of the belief that gods can and should be called out, that they offer AND need protection, AND the relationship of these theologies to the development of Roman self-identity.
I will return to this many times as I develop a section of my dissertation on theology of evocatio deorum.