  In the framework of a single scalar field quintom model with higher
derivative, we construct in this paper a dark energy model of which the
equation of state (EOS) $w$ crosses over the cosmological constant boundary.
Interestingly during the evolution of the universe $w<-1$ happens just for a
period of time with a distinguished feature that $w$ starts with a value above
-1, transits into $w<-1$, then comes back to $w>-1$. This avoids the Big Rip
jeopardy induced by $w<-1$.
