To jump into a hansom and order the driver to keep the four-wheeler in sight ought to have been the work of a few seconds, but it occurred, as invariably occurs when a hansom is urgently needed, that no hansom was available. The four-wheeler was receding at a moderate rate in the direction of the Grosvenor Hotel.

'Run after it!' said Hugo. 'I'll get a cab in the station-yard and follow.'

The quarry vanished round a corner just as they tumbled into the hansom on the top of Hugo, but it was never out of observation for more than a quarter of a minute. Through divers strange streets it came at length into Fulham Road at Elm Place, and thenceforward, at a higher rate of speed, it kept to the main thoroughfare. The procession passed the workhouse and the Redcliffe Arms. Between Edith Grove and Stamford Bridge the roadway was up for fundamental repairs, and omnibuses were being diverted down Edith Grove to King's Road. A policeman at the corner spoke to the driver of the four-wheeler, gave a sign of assent, and the four-wheeler went straight onwards into a medley of wood-blocks, which was all that was left of Fulham Road. The hansom followed intrepidly, and then its three occupants were conscious of a sudden halt.

'Bobby wants to know where you're going to,' said the driver, opening the trap.

There was a slight hesitation, and the policeman's voice could be heard:

'Come out of it!'

'We're following that four-wheeler,' Hugo was about to say, but he perceived the absurdity of saying such a thing in cold blood to a policeman.

All three descended. The cabman had to be paid. There was a difficulty about finding change—one of those silly and ridiculous difficulties that so frequently supervene in crises otherwise grave; in short, a succession of trifling delays, each of which might easily have been obviated by perfect forethought, or by perfect accord between the three men.

When next they came to close quarters with the four-wheeler it was leisurely driving away empty from a small semi-detached house which was separated from the road by a tiny garden. They ran into the garden. The one thing that flourished in it was a 'To Let' notice. The front-door, shaded by unpruned trees, was shut, and there were cobwebs on the handle, as Hugo plainly saw when he struck a match. They hastened round to the back of the house, where was a larger garden. A French window gave access to the house. This French window yielded at once to a firm push. The three men searched the ground-floor and found nothing. They then ascended the stairs and equally found nothing. The house must have been empty for many months. From the first-floor window at the back Hugo gazed out, baffled. Far off he could see lights of houses, but the foreground was all darkness and mystery.

'What lies between us and those lights?' he asked.