River-crossing logic puzzles: row a cast of animals and their snacks across without ever leaving a chaser alone with its target. Every puzzle is generated and checked solvable, with a clock that shrinks each time.
Tap a passenger on the bank where the boat is to put it in the boat, and tap someone in the boat to step off. Press Row (or tap the boat) to cross. ↶ undoes the last crossing and ⟲ restarts the puzzle; both are free except for the time they cost.
The chips above the river show who chases whom: an arrow from the cat to the mouse means those two may never be together anywhere the keeper is not — on either bank or in the boat. If a crossing would cause that, the boat refuses to leave, the pair flashes red and the line under the river says what went wrong. Nothing is ever lost; you simply try another crossing.
Each passenger has a badge showing the bank it must reach: an orange arrow means it still has to cross, a green tick means it is home. The puzzle is solved the moment every passenger is on the right bank — where the keeper ends up does not matter. The keeper always rows. The otter can row too (it has the same oar badge), but it keeps no peace, so chases still count when the otter is alone with them.
The boat has 2 to 4 seats, rower included, shown above the river. On some puzzles it also has a weight limit of 4 or 5: the keeper, the dog and the otter weigh 2, the bear cub weighs 3 and everyone else weighs 1, shown as dots under each passenger and as a load counter on the boat. Passengers step off by themselves when the boat lands; rowers stay at the oars.
A run is a chain of puzzles. Puzzle 1 has three passengers and 90 seconds, and every puzzle after that gets 2.5 seconds less, with no lower limit — puzzle 37 would have no time at all, so a run can solve at most 36. The casts grow from three to seven passengers, travellers going the other way appear, then the otter, weight limits and bigger boats; the fewest crossings needed rise from 7 to as many as 23. The clock only starts when you press Start run, and Practice gives you an untimed first puzzle with a Hint button. Your score is the number of puzzles solved, with the spare seconds you left on each clock added up as the tie-break.
Look for the passenger that sits in the middle of the chips — the one that is both chased and chasing, like a mouse that runs from the cat but nibbles the cheese. That passenger is almost always the first to cross and the one you will have to carry back once. The two ends of the chain can safely wait together, so the classic opening is: middle across, keeper back alone, one end across, middle back, the other end across, keeper back, middle across — seven crossings for a three-passenger chain with a two-seat boat.
Bringing someone back is not a mistake; it is the whole trick. The boat has to return anyway, and on most puzzles the only way forward is to carry a troublemaker home again for one trip. The same idea pays off with travellers who want the left bank: plan them as return passengers so the empty trips back do some work. With three or four seats, look for pairs that can ride together — two passengers with no chip between them make a safe crew, and moving them as a pair saves a whole round trip.
The otter rows but keeps no peace. Use it to free the keeper: when the keeper must stay on one bank to keep the cat off the bird, the otter can ferry a harmless passenger across alone. Just check the otter's own chips — it chases the frog and the fish, so it must never ride or wait with them unattended. Under a weight limit, count before you board: the keeper and the bear cub together already weigh 5, and so do the otter and the cub, so on a boat that carries 5 the cub always crosses with a single rower and nobody else.
On the clock, a refused crossing costs only the moment you spent, and the message tells you exactly which pair broke the rule, so testing an idea is cheap. A long wander is not: if you have rowed back and forth without progress, ⟲ Restart and think the opening through. Early puzzles leave lots of spare time, and that spare time is what separates two runs that solve the same number of puzzles; by puzzle 21 the clock is down to 40 seconds and every unneeded trip shows.