  For a constant $\gamma \in[0,1]$ and a graph $G$, let $\omega_{\gamma}(G)$ be
the largest integer $k$ for which there exists a $k$-vertex subgraph of $G$
with at least $\gamma\binom{k}{2}$ edges. We show that if $0<p<\gamma<1$ then
$\omega_{\gamma}(G_{n,p})$ is concentrated on a set of two integers. More
precisely, with
$\alpha(\gamma,p)=\gamma\log\frac{\gamma}{p}+(1-\gamma)\log\frac{1-\gamma}{1-p}$,
we show that $\omega_{\gamma}(G_{n,p})$ is one of the two integers closest to
$\frac{2}{\alpha(\gamma,p)}\big(\log n-\log\log
n+\log\frac{e\alpha(\gamma,p)}{2}\big)+\frac{1}{2}$, with high probability.
While this situation parallels that of cliques in random graphs, a new
technique is required to handle the more complicated ways in which these
"quasi-cliques" may overlap.
