`Driscoll walks into the tunnel, then, and meets the murderer. Mrs Bitton waits a short time, and follows, because she doesn't know Driscoll is still in the tunnel. Now do you see what we've got, Hadley? We've got Mrs Bitton at one end of the tunnel, Driscoll and the murderer in the middle and our good friend Mr Arbor at the other end. Haven't we?'
`Every time you begin to elucidate,' said the chief inspector, `the thing gets more tangled up. But that seems clear. Larkin said Mrs Bitton went into the arch at twenty-five minutes to two. Arbor bumped; into her on the other side of it at a coinciding time. Where's the catch?'
'I didn't say there was a catch. Now, following Mrs Bitton at a little distance is the eagle-eyed Larkin, who enters the tunnel next. All this time you must assume the murderer was still in the tunnel with his victim;. otherwise she would have seen him carry the body out. In the tunnel it's very dark and foggy. Mrs Larkin hears somebody moving. That is probably Arbor on his way out from the other side. Thus the tunnel is cleared of traffic. The murderer, who has been crouching there with his victim in a deadly sweat for fear he'll be discovered, carries out the body, throws it over the rail, and escapes., That, I take it, is the summary of events?'
`Yes. That's about it'
Dr Fell squinted down his cigar. `Then,' he said, `where does the enigmatic Mr Arbor fit in? What terrified him?'
Hadley slapped the arm of a chair with his brief-case. `He was passing through that dark tunnel, Fell… and when he was in such a bad state after he left us, the taxidriver said he kept repeating over and over something about a "voice”..’
'Tut, tut,' said the doctor. `Do you think the murderer leaned out and said "Boo!" to him as he passed?'
`I don't expect much from you. But,' the chief inspector said bitterly, `a trifle less heavy humour…. '
But he was not paying a great deal of attention to what Dr Fell said, Rampole noticed.; His eye kept straying to the mantelpiece, to the smashed figure on the hearthstone, and up again to the other image on the shelf. The doctor followed his glance.
'Let me tell you what you're thinking, Hadley,' he observed. `You're thinking: Murderer. Big man; strength. Powerful motive. Man capable of murder, from the emotional depths we saw ourselves. Man with access to crossbow bolt. Man who certainly knew about crossbow bolt. Man so far not even questioned about whereabouts at time of murder, Lester Bitton.'