The Night
Switchboard

What the game is

The Night Switchboard is a connection-drawing mystery — the classic hashi puzzle, also published as bridges or island-joining puzzles, rebuilt as a detective case. In the small hours something valuable left its case, and the handover was arranged by telephone. Every call in the quarter that night passed through one switchboard, and the operator's tally sheet survives: for every subscriber's line, exactly how many calls it carried. Nothing else — not who spoke to whom, not when.

You rebuild the night by laying cords on the panel. Tap the slot between two jacks once to lay a call, twice for a doubled cord, three times to cross the slot out as silent. The tallies force every cord by pure logic — and the finished web does more than satisfy the counts. As each line settles, its call slips print on the log with times and the operator's one-line notes, and the bureau's verified facts are waiting on the case file: which business line fenced the goods, the half hour the arranging call went through. Only one subscriber's line answers every fact.

Case procedure

1. Start with the crowded lines. A line whose tally is high against few slots has little room to hide: a tally of 8 doubles every one of its four slots, and a tally that equals twice its slot count fills them all.
2. Count each line's possibilities. Set a line's tally against the most its other slots could carry — every slot holds at most two calls, and a crossed slot holds none. Whatever one slot must make up, lay it. This interval counting is the quiet workhorse of the whole panel.
3. Respect the crossing law. Cords run straight and never cross. Every cord you lay silences the slots that would cut across its path — cross them out and enjoy it.
4. Never let a group seal itself. The night's traffic is one connected web. A cord that would meet every tally in a little group of lines while lines remain outside it can never be laid — the classic trap is two tally-1 lines side by side, whose connecting cord would strand them both.
5. Watch the call log. A slip prints when a call's cord is laid and both its lines' tallies are met. Half a night's traffic is often enough to start reading times against the verified facts.
6. Read the traffic against the facts. Clear every subscriber whose line fails a verified fact — no cord to the fence, no call in the stated half hour, the wrong number of connections. When one line answers everything, accuse — and bring the minute of the arranging call with you.

The rulings that matter most

• Tallies count calls, not conversations. A doubled cord is two calls between the same pair of lines and counts two at each end. The tally is exact — never a minimum.
• Cords join neighbours only. A cord runs straight between two jacks on the same row or column with nothing between them. A jack in the way breaks the line of sight; there is no slot through it.
• Cords never cross — and the panel turns cords red the moment any of yours do, so a night can never quietly go wrong. The same red flags a line carrying more calls than its tally and a group of lines that has sealed itself off.
• One web, no islands. Every call that night passed through the one board, so the finished traffic connects every line into a single web. No group of lines may close itself off with tallies met while lines remain outside.
• A single cord is not a promise. Tapping once lays one call; the second call of a double may come later. Check never flags a single where a double belongs — only marks that cannot be right at all.
• Verified slots are settled. Brass-marked cords come from the operator's tape and brass crosses were proved silent — they cannot be changed and never lie.
• Slips never lie. A call slip prints only when its cord and both its lines are exactly right, so everything on the log is true testimony. The times on the slips are how the hour fact is read.
• Calls count both ways. Every verified fact reads a call to or from a line equally — the tape never says who placed the call, and neither do the facts.
• No fact convicts alone. Every case is built so each verified fact leaves at least two suspects standing — the warrant always needs the whole night.

Choosing a rank

Night Operator (eight lines, four suspects) teaches the laws of the wires in about ten minutes, with two verified facts — the fence and the hour — and a small panel that settles quickly. Line Supervisor (fourteen lines, six suspects) is the full method: a bigger exchange, and a third fact counting exactly how many different numbers the thief's line spoke to, which only the finished web can answer. Exchange Chief (twenty lines, eight suspects) is the long shift: the fence fact now counts its calls exactly, a lookout line joins the case file, and only combinations of facts single out the thief. Bigger panels add more interlocking deduction, never unfair steps.

Fairness, hints and reveal

Every case is generated and then proved before you see it. The generator's solver must complete the whole night using only the deductions described in this manual — the same reasoning you use at the panel — which guarantees exactly one arrangement of cords fits the tally sheet and that no guessing is ever required. When an exchange needs more help, the bureau verifies another slot before the case ships; when it needs too much, the night is thrown away and regrown. The detective layer passes the same standard: the verified facts identify exactly one subscriber, and removing any single fact would leave at least two. Check flags marks that cannot be right without adding any of its own. Hints escalate politely: the first press names a deduction and the reasoning behind it; a second press points at the exact slot, and the cord is still yours to lay. Reveal unseals the operator's own record and excludes the case from your cases-cracked tally. Wrong accusations are stamped on the file; the case stays open — and naming the right subscriber with the wrong minute is its own stamped failure, because the magistrate signs only for the exact call.

Printing a case

Any case can be downloaded as a PDF pack built entirely in your browser from the same case number as the on-screen panel: the briefing, the verified facts with their rulings and every subscriber on the case sheet, one full switchboard sheet with tallies, line labels and verified slots sized for pencil work, and an optional answer key showing the complete traffic, the thief's line and the warrant. Bridges puzzles are print natives — a pack runs about three A4 sheets and suits classrooms, puzzle clubs and long train journeys, and the case number on the cover reopens the same exchange on screen.

Questions from the exchange floor