  We study the spectrum of the spin-boson model with two photons in
$\mathbb{R}^d$ for arbitrary coupling $\alpha>0$. It is shown that the discrete
spectrum is finite and the essential spectrum consists of a half-line the
bottom of which is a unique zero of a simple Nevanlinna function. Besides the
simplicity and more abstract nature of our approach, the main novelty is the
achievement of these results under "minimal" regularity conditions on the
photon dispersion and the coupling function.
