Presumably he at once concealed his cycle among the laurels where it was found, and possibly lurked there himself, with his eye on the house, waiting for Mr.Douglas to come out.

The shotgun is a strange weapon to use inside a house; but he had intended to use it outside, and there it has very obvious advantages, as it would be impossible to miss with it, and the sound of shots is so common in an English sporting neighbourhood that no particular notice would be taken." "That is all very clear," said Holmes.
"Well, Mr.Douglas did not appear.

What was he to do next?
He left his bicycle and approached the house in the twilight.

He found the bridge down and no one about.

He took his chance, intending, no doubt, to make some excuse if he met anyone.