presently stopped at a big double door.

"This is the Council Chamber," he said, as they entered a spacious
apartment. "You see that door in the far corner, over there? There's a
staircase leads down from that to the rooms that Bunning and his wife
occupy as caretakers--a back stairs, in fact. But nobody can come up it,
and through the Council Chamber, and along the corridor to the Mayor's
Parlour without first coming through Bunning's rooms, that's flat. As
for the other--well, it's still more unlikely."

He led Brent out of the Council Chamber and farther along to another
door, which he flung open as he motioned his companion to enter.

"This is the Borough Court," he said. "Magistrates' bench, solicitors'
table, and all the rest of it. And there's the dock, where we put the
prisoners. Now, Mr. Brent, there's a staircase--a corkscrew staircase,
modern, of ironwork--in the corner of that dock which leads down to the
cells. And that's the second way by which you could get to the Mayor's
Parlour. But just fancy what that means! A man who wanted to reach the
Mayor's Parlour by that means of approach would have to enter the police
station from St. Laurence Lane, at the back of the Moot Hall, pass the
charge office, pass my office, go along a passage in which he'd be
pretty certain to meet somebody, come up that stairs into the dock
there, cross the court and--so on. That's not likely! And yet, those are
the only ways by which there's access to the Mayor's Parlour except by
the big staircase from the iron gates."

"What is certain," observed Brent, "is that the murderer did get to the
Mayor's Parlour. And what seems more important just now is the
question--how did he get away from it, unobserved? If Bunning is certain
that no one entered by the front between my cousin's arrival and my
coming, he is equally certain that no one left. Is it possible that
anyone left by the police station entrance?"

"We'll soon settle that point!" answered Hawthwaite. "Come down there."

He opened the door of the dock and led Brent down an iron staircase into
an arched and vaulted hall at its foot, whence they proceeded along
various gloomy passages towards a heavy, iron-studded door. Near this, a
police constable stood writing at a tall desk; the superintendent
approached and spoke to him. Presently he turned back to Brent.

"There's nobody that he doesn't know has been in or out of this place
during the whole of the evening," he said.