At that hour it awoke him with extreme difficulty.

He awoke Erebus with extreme difficulty.
Five minutes later they were munching bread and butter in the kitchen to stay themselves against the cold of the bitter November morning; then they sallied forth, equipped with rags, string and the bottle of valerian.
They bicycled to Muttle Deeping.

There the Terror poured valerian on one of the rags and tied it to the bicycle of Erebus.

Forthwith she started to trail it to the cats' home.

He rode on to Great Deeping and trailed a rag from there through Little Deeping to the cats' home.
When he reached it he found Erebus' bicycle in its corner; and when, after strengthening the trail through the little hanging door with a rag freshly wetted with the drug, he returned to the house, he found that she was already in bed again.